After some pondering it seems the spring clamps/clips would interfere with the steel helper springs so that idea is now out (although maybe the cross bolts could be taken out so it could fit between the sides of the clip). The shocks with springs around them, it turns out, capture the coils at both ends so the spring will tend to keep the suspension at a fixed point, it will pull up on the axle when the suspension droops and push down on the axle when the suspension compresses. This seems like it would hinder droop too much.
So I've pretty much decided to get some air shocks that can be pumped up as needed or left unpressurized when no extra load capacity is needed. After cross-referencing some part numbers and specs it looks like the Monroe Max-Air (part number MA728) shocks could work. They would not limit suspension compression and would allow 9.125" of travel vs. the 10" with my present shocks, good enough given that my rear suspension doesn't seem to reach the end of the travel of the current shocks. These are made for some Cadillacs and Isuzu Pickups.
It seems they come with mounting studs in the bushings which I would need to take out. Also, the Monroe spec sheet shows that the bushings are 1 5/16" long with a 5/8" hole, the same as the upper bushing for a stock YJ. So it seems it should work fine.