First off, 105#'* actually have a lower spring rate than stock L36, so they theoretically will cause less wear. 90#'* (aka LS6) springs have a higher rate, so should cause more wear. This is the primary reason I shy away from 90#'*.
Second, I had considered just what you are talking about, shimming stock L36 springs with ER/SR rockers (instead of buying 90#'* or 105#'*)...to shim enough to get the kind of seat pressures 90# or 105#'* can give, you will coil bind your stock L36 springs.
If you need springs and retainers pronto, let me know. I've got used (but tested and passed) 105#'* and CC retainers I've collected for my own head job, but that job ain't happening until at least Xmas break (so I've got time to replace them). I could ship them to you or to TJ.
2004 Buick Lesabre Limited, Gran Touring; Bone Stock
1998 Buick Lesabre Limited, Gran Touring; Mods: Poly sway bushings/endlinks, Tru-Cool trans cooler, Thrasher shift kit (med), PLIM, front PEM; Mods in progress: Alot of stuff, but slowly...