With a little searching on the forum here you will find great diagrams to get ground, USB data in/out(twin gold pads underneath battery), and USB 5v.
The USB system if just ripped off can be repaired as long as you can stick the port down physicaly and string the wires.
The only USB you cant fix is one which has been static shocked, even then there might be hope but it is tracing down the fault on an old SMD board using many EOL components and without a schematic.
You can also just do everything filesystem wise using SSH and SCP for file transfers and get a dumb Li-po charge board, wrap in kapton tape, and hide it inside the phone or a Mugen bulged battery cover if you can find one. On second thought put the charge board under the battery cover and run wires through, cramming stuff inside flexes the system board and leads to the dreaded dead SIM de-balled modem chip.
(edit)
I think this is the first time I have seen this schematic, as we approach the heat death of our N900 universe a gasp of hope.