Modifiy collision size with triggers

I got this item called Tome of Portals, that when used, teleports the Hero into a closed area (Tower Defense), and since most people do mazes, I don't want the Hero to be able to block a path so the mobs go wild and attack the towers...

Any idea how to fix this? I thought "Turn Collision On/Off" trigger would work but from what I have read it doesn't work.

You can give the hero a very small collision size, or just make him flying with height 0 and no pitch/roll values.

well, the hero is supposed to have 32-48 collision size when its not in the TD, that's the whole point.. but when it enters the TD, it should have 0.

Turn collision off does work, but it means the bloke can go anywhere (if you force it).

ah, good... the entire TD is one huge region...

got a...

Unit leaves Region-trigger incase some unit should try to leave it (like the builder)