how to make a portal open in just the end?

no bumping

I was wondering if this was possible too..

The only way I can think of to do this is to add a check to whatever block you use for the portal frame.. the check would only allow them to be only in a certain dimension.. so use the when block added option and use an If dimension is the end then place block, else place block and then remove and send message to user saying it can't be placed there.. also checking for open space..

I'm about to go to bed right now, but If you wait till tonight after I get off work I can throw together a workspace with what I described above that should be exactly what you want..

Or you can try to get it on your own before I can :D..

Something like this.. I did it quick because the bed thing..