You would have to replace or hotwire the ignition to bypass the keyswitch, so you'll need a schematic of the ignition, or at least schematic of how it connects to the car itself, then you can do anything you want. By the way, make sure that the signal you use to turn the car on etc.. is very very difficult to reproduce and impossible to reproduce accidentally, or you'll come back to your car one day with an empty gas tank and a dead battery =) Also make sure you have at least two or three FOB's.
We don't have a key for the doorlocks on our car and I'm waiting for the day when the keyfob runs out ofbatteries =P Luckily we had a remote start added to the car so there's two fobs on the keychain, and one in a drawer at home.