Yea, that would suffice. Just be sure, to not use battery - (minus) as ground - it's marked wrong way in 1st post of thread You've linked. Shouldn't burn anything, and probably would work OK (battery - is connected to ground plane anyway), but it's still better to use ground from testpads, just like other things.

As for contact pins, I woudl recommend spring-like connectors - just like device is using for speakers, audio jack, etc (You will notice it upon disassembling N900). You can use very small, "normal" springs too - just be sure, that in any conditions, they won't bend and short some random testpads...

Also, remember, that You need *both* battery (either real, or fake, via something connected to battery pins, with 3rd battery pin connected to ground via 100k Ohm resistor), and 5V/Ground "fake charger", for establishing USB connection.

Easiest way, IMO, is to take upper part of battery (this one with pins - as a bonus, it contains BMI Pin shorted to ground via 100k resistor, already implemented), then put it on piece of wood or plastic cut in shape of battery cell. This way, You will have "fake" battery, containing pins for contact with testpads (of course You need to manufacture those pins Yourself, on Your fake battery).

/Estel

// Edit

Or search for "N900 JAF" cable - it should be exactly what You need, and cost around 10 USD max AFAIK, it's exactly "fake battery", with springs for testpads already in place. you would just need to tear it's cable (it's standard RJ45 plug, useless for Your case), and test with multimeter, which one corresponds with battery +, ground, 5V, USB DATA + and USB DATA -; then connect it to appropriate things (and isolate other cables).