I've been able to do the following trick and get similar results every time:

1. Send a scout into a system known to have hostiles
2. Have a task force ready to jump to that system
3. Have the scout "run around" the system - the hostiles will follow attempting to destroy the scout.
4. Send in the task force
5. HOSTILES WILL CONTINUE BRAINLESSLY FOLLOWING THE SCOUT WHILE THE TASK FORCE BEATS THE CRAP OUT OF THEM. HOSTILES will not FIRE ON TASK FORCE UNLESS SCOUT IS DESTROYED.

Need some AI work here.