I am a rabbit breeder and I occasionally sell rabbits to other people. When changing food and often due to extra treats that new rabbits are given, the rabbits will suffer from a condition called bloat (warning: link contains images of dissected rabbits). It is difficult to convince some people to spend $100 or more on a vet visit for an animal they can replace for $50. So, sadly most people will just allow nature to take its course, which is a painful way to die. Is there anything I can do to relieve this condition without having to consult a veterinarian.
Gastric dilation, also know as bloat, is a veterinary emergency. Rabbits, as you likely know, are not able to vomit and so cannot void the contents of their stomach if the normal outflow is blocked for any reason, which may not always be physical, apparently stress and severe stomach movement can cause this as well.
Unfortunately, according to Blackwell's Five Minute Veterinary Consult for small mammals (second edition - Section IV, Chapter 186) , the rabbit requires immediate medical therapy involving gastric decompression using intubation and surgery is likely required to treat the condition if intubation efforts fail to relieve the issue. It is also possible that decompression may be required several times depending on the actual causes of the bloat.
So, unfortunately, the answer to your question is no.
It is often said that "An ounce of prevention is worth a pound of cure". I assume that since you care about the welfare of the bunnies and that you are dealing directly with the new parent that you are screening for appropriateness of the home and providing eduction to the new family, so I will not address those points.
In our (my wife and I) volunteer capacity we almost constantly have bunnies staying with us in our home. We also realize that dietary changes can be fatal. For visiting bunnies, they arrive with the type of food they are already eating. We keep them on that diet the whole time. If a bunny will be changing diets while staying with us, they stay 100% original the first week, then 75/25 the second week, 50/50 the third week and 25/75 the fourth week. On the fifth week, they are 100% new diet (assuming no issues). See this question for more on changing your rabbits food type.
In your situation, I would recommend including a supply of food with the bunny when it is placed in its new forever home. Include instructions on how to change the diet, what to watch for and what to do if there is a problem. The best thing you can do is provide the new family with the food, and directions to prevent or limit the occurrence. Presumably you are feeding breeder-type food, which is generally too rich for maintenance of house rabbits in a home environment, so staying on the same feed is not a viable alternative.
For treating gas or anything that is even remotely digestive related, I always start with a good dose (half a table spoon OR 1.5cc) of baby gas drops "Little Tummys Gas Drops" is the name brand I usually use, but if available have also used generic brands. According to my vet, there are no counter indications to using it, and there are no dosage limits. So using as often and as much as you want (common sense) is OK.
My bunny that usually has the problems will often lick the flavored kind from a table spoon. If necessary, I use a syringe to get him to drink it. Anytime a bunny is having a diet issue, 'GI stasis' is the first concern, so keeping things going through the system is important. If the Gas Drops have not caused a return to eating/drinking in an hour or so, I begin forcing feeding baby food (carrots, banana or squash) and water. I continue this every 2 - 4 hours until he begins taking food/water on his own. Usually he is back to normal in 6 to 48 hours.
I have had some recommendations for subcutaneous fluids and have used them sometimes. In my personal opinion (and many will differ) for ailments solely related to digestion, the mouth is a better avenue for all but the most severe cases that are primarily digestive in origin.
This answer is from personal experience, contact your veterinary professional before making any oral drug choices for your rabbit.
When I first brought home my flemish/silver fox girl she was about 2 months old. I noticed the first couple days that she looked a little funny a small rabbit that seemed to have swallowed a balloon trying to run around.
Anyway, when I called my vet and described her symptoms, she said that she most likely had bloat and that I was to remove all food (dry or green) and feed 100% Timothy hay for 2 weeks. My little girl started expelling gas like no body's business which made her smell for the next week but she was fine.