FYI, I am working my way now thru the sprint extended rom with an eye on making it into one or more OEM packs.
So far, several of them are just registry settings (which is sure easy)
I am using the most recent sprint extended rom cabs, and
http://www.freewareppc.com/utilities/msceinf.shtml
Working fine so far. But sadly, time to get going on the day job
Anyway, when done, you should end up with 1 OEM pack you build into your OS ROM *for SPRINT 6700 only* then you can just nuke your extended rom and use it as you want. It will not contain any PRL/PRI stuff, as that's a simple cab you can run once after a cold boot, and frankly your PRL is in the radio anyway, so you don't want to change it (potentially back to an old version!) every time you hard-reset.
I will keep track of what I'm doing to make the OEM(s) so we can get a guide going.