So, its taken me a while to realise this, but I can just do the following, using ROMManager:
- Backup phone - optionally, copy backup off phone to store safely.
- Boot into custom recovery from ROMManager.
- Install update.zip - this will be the installer for the "next" android ROM.
- Install super user zip from sdcard.
- Reboot phone.
- (Re)connect USB to PC.
- adb shell and rename the install-recovery.sh so android won't keep replacing the custom recovery (see earlier posts).
- Reboot to test that previous step is good.
- Marvel at latest set of goodies.