Doomstacks of 15 fleets at max capacity seem to me to be contrary to the strategy portion of this strategy game.
If it were the only strategy and extremely dominant in every situation, then I would agree with this, but that's really not the situation we're in. Doomstacks have one very clear weakness, which is the fact that they're very slow at conquering systems.
A person who insists on running around with a doomstack will lose a war against a person who counter-attacks with two or more fleets that attack from multiple angles because they simply can't conquer quickly enough. If there's not enough space to maneuver around when doomstacking is he correct choice. (Which is the actual problem, there just isn't enough free space)
But for the actual question: I think that's not possible. There's no way to interact with hyperlanes in that way.
Unfortunately, there isn't even an on_action for hyperlane travel, so I don't think you can't even do any good workarounds.