You can put thermal sensors on your missiles and launch them at a waypoint near the enemy. If the enemy is close enough once the missiles reach the waypoint and their thermal emission is strong enough, your missiles will engage the enemy (Yes, those are quite some _ifs_)
You may need a rudimentary missile fire control system, but, IIRC, you will not need one with enough range to reach the enemy/waypoint.
Missiles _do_ have a thermal sig, but it is usually extremely small, so your regular thermal sensors notice them right before they hit you. To defend against them, res-1 actives are definitely the way to go (remember to look at the range, size-6 and smaller missiles can be detected, not the nominal range - and this goes for both, active sensors and missile fire controls)