router external antenna mod

I have a Belkin N1 wireless router. The signal extends up to 1400 feet (depending on # of walls in between). The router has three external antennas. I want to remove the center one and hook up a stronger antenna. Hopefully one that is on my roof. I have opened my router and found that each of the three antennas is attached to the router's circuit by a small connector (the size of a pin). My question is, how can I connect another antenna to that plug? can I sever/cut the center antenna's cable in half and join that cable to annother one which has a stronger antenna outside? Or can I but that connector somewhere and hook up a pigtail and then an external antenna to it? how would I go about this? Thanks