Maybe someone more familiar with court operations can correct me here, but what's to stop Mr Stewart from arguing that 922(o) is unconstitutional by the test established in US v Miller? It shouldn't be hard to show the suitability for military/militia use of machineguns.
The 9th would deny him this argument (they already have said that the 2A does not guard an individual right in Silveira, and cited thier Silviera decision in denying Stewart's 2A claims the first time, on his appeal of his conviction for possession of firearms by a felon.
When the 9th upholds his conviction on the machineguns (which they will), Stewart can then make an appeal to SCOTUS based solely on the Second Amendment. And unlike in Silveira, there wouldn't be any 14th Amendment issues to clutter things up, since 922(o) is a federal statute.
This would be a new appeal, since the one that was just remanded today was an appeal by the government.
Looking at the odds, I'd put Thomas on our side for sure, with Scalia (based on his reverence for precendent) and Rehnquist's replacement likely on our side, with the 4 big libs (Ginsburg, Stevens, Breyer, and Souter) on the bad side. That would mean we'd need to get O'Connor and Kennedy. Just one for cert, both for the win.