I don't think spinning the barrel nut will help at all, all that will accomplish is loosening or tightening the barrel nut. IIRC they mount like a Troy handguard, so it slips over the barrel nut and pushes all the way back to the upper then clamps down.
The options I see that you have are:
1. take the handguard off and file the handguard down where it hits the pivot pin to relieve it. (more work and you have exposed metal but full contact area between upper and handguard)
2. put a small metal shim between the handguard and the upper (a small washer around the gas tube would work perfect, it would likely only need to be 0.5mm thick) to get the extra space. Then clamp down the retainer screws. There should be more than enough length on the anti-rotation tabs that a shim could be added. This of course means less contact between the upper and handguard, and it may flex.
Bump for more ideas though.