I've installed a few factory GPS systems in my 300m and PT Cruiser DC and never had an issue with the antennas. Just use two-way tape and stick the antenna inside the console near the top, away from any metal. The antenna sees through the plastic of the dash no problem.

Put an RB1 in my PT six months ago, for instance, and did this. Just taped the antenna and shut everything up again. No muss, no exposed wires. Get perfect sat reception, usually seven of eight or whatever. Ran with the antenna exposed on top of the dash as well and had the same results. So you really don't need to bother with the external leads or whatever. Just leave the existing in place. Additional hassle you don't need.