Absolutely no! I must admit - it was late, when I've replied last time, and I missed this idea in his post. Unless You like smell of fried electronic at the morning, never do that.

You need to either connect ~4V power supply to battery pins on "fake battery", having BMI pin connected to ground via ~100kOhm resistor (if it's done this way, one may leave it - if not, tear connection apart, and re-wire everything), or do other trick, that I will describe on next paragraph. 4V power source may be hard to get (until someone like to connect 5V power supply through chain of diodes, until voltage drop to 4V - not so good idea), but this way, You don't need any other elements.

Easier, and IMO, more practical way of dealing with it, is connecting real, cheap BL-5J (any will do, even crappiest 400 mAh one) to battery pins in "fake battery", at the same time, breaking any other connection to battery pins.

5V power supply goes to pin that touch 5V testpad under battery, and ground, to ground.

This way, when you enter your docking station's fake battery into N900, You will have it working on battery (this real BL-5J, mentioned earlier), and charging, at the same time (thanks to 5V connected to test-pads). This way, capacity of BL-5J doesn't matter, as it is in fact running on charger power, with battery acting as big capacitor. If You do it smart way, You can every prepare easy-replace slot for that BL-5J, so you will be able to charge *any* BL-5J via N900 and your docking station.

All of the above, without USB port at all. Furthermore, if you mod "fake battery" to have pins for USB Data + and - in correct place, You will also have USB connection available (for flashing, or regular, every-day use, like mass storage mode, or hostmode, or whatever you feel fancy).

/Estel