I see that there are 2 sling options for CMP and NRA service rifle competition. The Garand web sling that only attaches from your arm to the front swivel, and the leather 03 Springfield sling that attaches to the front and rear swivels with your arm in the loop.

My question is, can I configure the leather sling to fit like the web sling ? No attachment to the rear swivel.

Yes, you can unhook the “frog” (double-hooked metal end piece), unthread the rear of the sling from the rear swivel, and then just tuck the unsecured tail into the sling cuff around your upper arm.

Look up "no pulse" sling setup on YouTube.

Or get Jim Owens' book "Leather Sling and Shooting Positions". He explains it in there too.
Jon