Yep, one keyboard.

Using keyclone you generally put your WASD movement keys on do not pass but leave your arrow keys off DNP. So your caster is merrily following the melee dude who you are controlling with WASD. You start to approach a mob, you tap the down arrow, which causes both toons to take a step back and breaks caster's follow. Then the melee runs in and the caster stays put.