Easiest way I see it is to make it a transport unit that can load units within 1 range.
You can get the loaded units from trigger and then you can teleport them.
That way you can also cancel the teleport when you right-clicked on it from far away.
Thanks - this worked like a charm.
For anyone wanting to do this aswell, all I had to do, was to dublicate the Warp Prism - Load-Unload (Shuttle) ability (comes with both model and sound actors so that's the easiest). Go to the (Basic) Ability: Target Filters and check the flags all the in the bottom (Ally, Enemy, Neutral, Player).
Then you give the ability to your portal unit, and use a trigger like this:
Portal Trigger Events Unit -Portal [54.00, 122.00] Loads cargo Local Variables Point = Point 013 <Point> Conditions Actions Unit -Move (Triggering cargo unit) instantly to Point (No Blend) Camera -Pan the camera for player (Owner of (Triggering cargo unit)) to Point over 0.0 seconds with Existing Velocity% initial velocity, 10.0% deceleration, and Do Not use smart panning
Now, whenever you right click to move to your portal unit with a unit, the unit will load into the portal when it gets within range, and the trigger will teleport the unit to your desired location.
EDIT: A little side-note. The ability has the Visible flag marked as Required in the (Basic) Ability: Target Filters, which would not allow cloaked units to use it. So set this to allowed, to be able to use it as a cloaked unit.