You are fighting a lost cause with a ROM dump...the concept sounds a lot easier than it is. It would be equiv. to moving a copy of Windows Vista from one machine to the other without install disks (just copying).
The only major difference in the ROMs should be the PRL, which tells the phone what towers to use. From the little research I just did, Bell does not provide OTA PRL updates (which is strange). Many people suggest going to a store, which may be a catch 22 for you. I do seem to remember a third party website that let you download PRL updates and transfer them to your phone, although I couldn't find it easilly via google. Maybe you can find it, or someone else here can chime in...
**Edit**
Here ya go...not sure if it will help, but check it out...
http://www.corolada.com/prl/
**Edit #2**
My bad, that was only US carriers. I found a link to a Bell PRL on another site....you may need to register to download...
http://forum.xda-developers.com/atta...0&d=1201660410