Use RSD Lite and flash the 2.1 update 1 SBF. Then you can try to ignore the nag screens for the update that'll hit your phone in the next couple of days, if not immediately, and deal with it telling you to update every 20-30 minutes.
Yeah, you'll lose everything.
I've stopped hearing complaints from people unless I'm expressing an opinion anymore. People have reinstalled updates, gotten used to the changes and improvements, traded their phones back to Verizon to get ones that weren't borked on update, or rooted and installed custom ROMs. Those really, seriously, are your only options at this point. This cannot be said more clearly and no other options will present themselves unless you go flash SPRecovery (rooting your phone) and then install a specialized update.zip file that blocks OTA updates (still rooted). The problem, you see, is that this requires rooting your phone, which you seem reluctant to do. Furthermore, by flashing the SBF to get back to 2.1 you've lost everything on the phone.
So, to wit:
Reinstall the update, adapt to the changes, or root. Verizon probably won't take the phone back without it boot-looping or you dunking it in water, and there's no guarantee that any phone you get won't come with 2.2 preinstalled or the update forcing itself onto your phone as soon as/before you get it home.