Thank you for your inquiry, but unfortunately we do not have a professional wildlife rehabilitator through the MSU Extension Ask an Expert program. It sounds like you have done an excellent job caring for this rabbit, against all odds! Since you are in Washtenaw County, I recommend contacting the Michigan Friends of Wildlife organization. Glancing at the page it looks like they don't currently have a rehabilitator specializing in rabbits, but it can't hurt to call; hopefully at least they can guide you on when to release the rabbit. They also provide some general information on rehabbing rabbits and also through this group.

If the above linked information doesn't help, the Michigan DNR provides a comprehensive list of statewide wildlife rehabilitators and you can find several specific to Washtenaw County.

Best of luck!