Is there any way of circumnavigating the seat weight limit in an R22?
No. for a Beta I think you will find that the minima solo weight (135lbs with doors on) is designed to keep the Cof G within limits with full tanks, aux installed as well.
The maxima (240lb per seat) is designed to preserve the integrity of ones vertabrae. (max design weight)
The empty Beta weight will be around 861lb and the minima allowable AUW is 920lb. at minima AUW the aircraft should autorotaate at right on the bottom red line (90%) at about 52knots in standard ISA. This will give you full travel of the collective to arrest descent.
so you see it is all very simple, if you are petite and beautiful as all petite fenminine people would be, then carry enough weight to preserve the CofG and you will never fail to safely conduct an autorotation should the need arise.
cheers tet