Although it is annoying that bracing of this sort would be difficult if not impossible to implement, I was wondering if one might get somewhere with deployment of heavy MGs like the M240. Unlike regular guns, including the M249 SAW, the portable MGs are almost unusable from a standing or even crouching position. This makes them almost useless unless you are prone on open ground (no grass or obstacles to obscure your view).
I was wondering if it would be possible to have a "deploy tripod" command which created a vehicle in which you could sit and fire the very much more stable gun (which would allow you to see over grass and small obstacles). You'd obviously be able to undeploy the weapon again, which would put it back in your inventory. By using the vehicle approach, you don't have any issues about standing up with a deployed weapon that used the replacement weapon method described above.
You could also allow an assistant machine-gunner/loader position in this "vehicle" (which would automatically move MG ammo from the loader's inventory into the vehicle's inventory when a reload was required). The major reason for a loader, though, would be to eliminate reloading times by hooking together ammo (implemented by, when the magazine is empty, removing the weapon from the vehicle and replacing it, which should instantly reload it). Having a separate position might be difficult, since if you weren't using a loader you'd still need the free "space" at the left of the weapon in which to to put one. If you implemented this re-loading feature, then it would be worthwhile having a "deploy bipod" action, so that you could use the loader in the prone position too (might still be worthwhile, since you could make the non-bipod MG still pretty unwieldy in non-deployed use).
Anyway, I know nothing about making models or configuring them, since I'm more of a scripting fellow, but I thought it was worth discussing if this method was possible.