I pulled this idea from when I had my GTO and the adjustable coilover kits featured a threaded, collared "spring pad" to allow adjustment of the rear, since it was a trailing arm design with separate spring and shocks. I was looking at the rear axle and was wondering why this couldn't be done to allow some adjustment on to the rear for those people who have a JBA Adjust a Strut. It was a little quiet today at work so I threw together a couple of quick cad drawings. What do you think:
The Base Pad:

The Collar which actually supports the spring:

Assembled in the "Stock" Height position:

Assembled with Lift:

The one issue I guess I could see is coil bind since you are using a shorter spring to try and achieve a taller lift. One idea is that you could make the Collar have a solid top instead of open so that as you raise the spring, the contact point for the bump stops also raises so the effective distance stays the same. This may also eliminate the need for hockey pucks with a taller tire. I could also be making stuff up, you tell me.
I see this as being the same thing as adding more isolators but is fully adjustable and looks super epic in red anodized aluminum