Besides the shortened VFGs, I've seen set ups where guys use a 90 degree side-mount attached to their weak hand side rail on an AK to allow putting running a VFG offset enough that it's not in the way of a mag change.
No idea how well that works, never tried it, but think the assymetrical set up would annoy me.
Also +1 on what Nalioth and others said about pushing the VFG further forward as well -- further forward is (mostly) better in any case, giving you more control on the muzzle.
Alternately, just get a wooden pistol gripped fore-end like various countries put on their issue AKMs back in the day (thouh that may end up costing more than a rail plus VFG). Those will definitely allow for mag changes with no problem.