I have one usb device that will not work because of the limited usb current. I don't want to add a powered usb hub (saving cost and space) and I don't want to solder on my pi (polyfuse mode). Can I just "bridge" the 5V to the USB device?
I guess that should not be a problem, for the USB device certainly not a problem. Depending on the USB implementation on the RPi it might not detect your device because it doesn't draw any current. If that is the case you can use a resistor to draw a little current on the USB output. (Put this resistor between the unused 5V and GND outputs on the USB connector)