I never had a NICS check run on me when I bought my MG with a trust.
The ATF started requiring it later, but that doesn't mean that it is required by law. Just like MSP said lowers were illegal until they were forced to change their position.
In fact, I don't see any legal reason why I couldn't sell my trust by adding you and dropping myself and skip the entire process. I would guess the ATF would try to nail you, but I haven't seen any statue that restricts buying/selling trusts.
You can change trustees but you can't change the grantor. It's still your trust if you remove yourself as trustee.