How would a trust solve anything? The law (or the regulation) is that it is legal for an individual to make (manufacture) his/her own firearm. The BATFE has graciously allowed this to be interpreted that, as long as the owner performs at least 20 percent of the work him/herself, it is still considered to be making your own firearm.
How is a trust (which is a legal entity that has no physical body) going to operate a lathe or a milling machine?
I'll be honest -- people who do stunts like these "build parties" and try to push the envelope on the law/regulation are not doing the rest of us any favors. It's only going to take a couple more cases like this before the BATFE just pulls the plug on "80 percent" receivers and rules that if you didn't make the entire gun yourself, from scratch out of a solid block of steel or alloy, you didn't make it yourself and it's not legal.
As a frustrated tinkerer who would love to do an 80 percent receiver one of these days, seeing people trying to game the system royally [irritates] me. They think they're being cute and smart, and all they're doing is undercutting those of us who are willing to do it the right (legal) way. They're going to ruin it for the rest of us, and I think that's truly sad.