Blockade strategy?

[SpaceBadger]

Suppose you have some warships in an enemy system, you have troopships but they are busy conquering the enemy homeworld, and you want to blockade another enemy world to try to force surrender or at least prevent new enemy ships from being built there. What strategy can you use to keep your warships from just glassing the place?

I tried making a new strategy called Blockade, with the box checked for Don't Fire at Planets. It didn't work - they glassed it anyways. I thought of using Don't Get Hurt as the movement strategy - would probably work OK if no enemy ships moved into that sector or were built there during the blockade, but would likely get the blockaders killed if any enemy ships were present.

Any more ideas? Is there a way to blockade on purpose, or does it just happen when your ships lack the muscle to glass the place within 30 combat rounds? Or do you just have to leave the place alone until your troops are ready to move in?

SpaceBadger