Launch a couple squads of 3 scouts each loaded with mines. Weave your way over
or around the enemy lines at the very beginning and find their flag. He's probably
just sitting where he started while he preps planes or he's set a course straight
north or south. Either way, he's not paying much attention to your scouts. If you
survive well enough to get to him, drop your mines far enough ahead in his path
that he won't see them dropped. If he's still just sitting there, drop them a little bit
in front of him so he'll hit them when he finally does start moving. Then keep your
scouts over their lines until they have to come back.

Note: It's a long trip, so babysit your planes to prevent them from automatically
returning when they run out of fuel. It's most likely to be a certain one-way trip for
them.

It's worked more than 50ish% of the time for me.