I don't know about reinstating miles, but I recently used FTD to send some flowers for Valentine’s Day to top off my daughter's MP miles. I purchased from FTD with my information but put her MP number in as the MP account to credit the miles to. She has a different last name from me and the miles did post to her account. It took 4 weeks for them to show up in her account but FTD claimed up front it could take 4-6 weeks to post.

So, you definitely can post miles to another account. I just don't know whether or not this would work for reinstatement but it could be worth a shot.