I used to do this on my 1000 between 1.3 and 2.x. The trick is to use a version command on one of the libraries from the ROM in your startup-sequence. If it's the 3.x version, then you re-assign everything to the 3.x partition. Otherwise you just go ahead and continue into 1.3. I can't find my old 1000 startup disk right now, or I'd post the correct syntax.
