How about building a flashing/usb connection rig? I've been thinking about this idea for a while. The schematics show a FS-94 flashing rig, but there seems to be very little on the internet about them.

They can definitely be used for the purpose of flashing though, as this blog shows.

I bought one of these of ebay. The box is plastic and the pins are springed so that when you plug in the box the contact is firm but in the wrong place for our purposes. But it does provide the dimensions of a would be flash box made out of metal, or perhaps it could be lined in foil and grounded? The protection circuit could then be inside the flash box, and a battery would be fixed beneath the box.

So from bottom up, you would have battery>>flash box>>n900.
You would then have a microusb connector mounted on the box.

This approach would have the benefits of allowing phones with pcbs too far damaged for repair to be repaired, it would also save you from having to open your phone, and stop it from looking like a bomb when going through customs!

Obviously this couldn't be carried around in your pocket, but for flashing/usb transfers purposes it would do great.

If someone could make a properly fabricated pcb that was 5-10mm thick then maybe a thin box could be made that would sit between a battery and the phone and could sit inside a mugen battery cover modded with a microusb port. This could be the complete solution.