[Alneyan]

The best you could do would be to force the event "Warp Closed" to always occur, thus collapsing any wormhole once they have been opened. (I didn't manage make it actually work however, but there is no love lost between events and myself)

Afterwards, you might want to add the "Prevent nasty events from occuring there" ability (don't quote me on the name of the ability, for I have forgotten its proper name). It would only work if there were more than one wormhole at a given time however, as otherwise the event would still occur in the same system, since it would be the only proper target.

But this is a mere ranting, as I could not get the above to actually work in a game. *Grumbles*