relays

That's a pretty simple task -

Look up your car in the wiring database and purchase one relay for each ignition wire and each accessory wire listed.  You may want to pick up an extra relay or two in case there are some non critical ignition/accessory wires not listed in the database (only the wires needed to remote start the are generally listed).

Then, wire up a toggle switch to control all the IGN relays and one to control the ACC relays.  If you want to get fancy with it you can set up the starter relay to drop power from the ACC relays.  You will then need some sort of push button or intelligent control module to control the starter relay.