Did you talk to the CFI about this? Because you're not the only one that will have this problem, and it might be a good idea for the FBO to come up with one solution, instead of 100 renters with each their own.
For example: get rid of the habit of fueling it full up after each flight. If the aircraft has a wet rate, it doesn't matter anyway. If the aircraft has a dry rate, use the markers instead of full.
Or do what we did in the DA-40 at our club (same CofG problem): fill a bucket with sand, exactly weighted so that with two standard adults up front, full fuel, and the bucket of sand in the back, you were exactly within the envelope. The bucket was sealed, marked with its weight, its purpose and the callsign of the aircraft, and was normally left on board in the rearmost cargo compartment (with a visible tag sticking out the finger hole of the cover of said compartment). If you don't need it you can take it out and leave it in the grass next to its parking spot, as long as you put it back in after the flight. (We need 17 kilos so it's just about doable getting it out and in without getting a back injury.)