Block GUI procedure needs the GUI to be open

I have a very simple goal.

My current mod adds multiple new biomes, which can be teleported to using consumable potions.

It'd be annoying to make everyone use a hard-to-obtain potion for every single teleport, however, so I'm trying to create a block which does it for them with unlimited use when a redstone signal is activated.  It checks the first slot for the teleportation object, which dictates what dimension the player will be sent to (Or it will fail if the objects in the slots are invalid), and the second slot for fuel (which will not even be consumed), usually a diamond.  If both slots are valid, it teleports the nearest entity type player within a 7 block square cube.

My first problem arose with attaching it to the teleportation block.  It says that its 'missing dependencies' so I had to do a workaround (the procedure requires an active redstone signal and you punch the block to activate it, which worked).  But that's fine, this is also interesting.  My goal here is just not to require the player to have the GUI open in order to be teleported, because it'd be funny to unwillingly send your friends to the dark dimension because they fell into your devious trap.

But you do need to have the GUI open, because a part of the procedure is 'Get item from slot X of the current GUI of Event/Target Entity' and I can't find an alternative.  Is there a workaround or a fix?

While I'm here, I might as well mention my other problem along the same line of thinking.  I wanted to have things which would have different effects depending on what dimension you're in, but if I try and do 'If - ID of dimension Event/Target Entity is in = X' then there is no X.  I cannot specify differences in the procedure based on whether or not the target is in dimension X, Y, or Z.