I rotated the front sling mount 90 degrees to the left from the factory position (remove snap ring, reposition sling mount, reinstall snap ring) and installed the VCAS sling. Works great.
I see that this is a old thread but as a new (Sep '09) M4 owner I will give my findings.
I went with a VCAS COBRA PADDED VERSION in black from blueforcegear. (Wanted the Cobra release buckle)
Not cheap but very functional.
I am a right hand shooter and rotated the M4 front sling mount from 270 degrees (tag down) to 180 degrees (tag to the left) and the resulting sling position is what I wanted.