ah....so I just spotted the baleful realmgates new rules in ghb18. Just let them jump through, with a wizard as chaperone...no rolling dice to see if any get lost. That’s great for slower armies and adds some nice tactical stuff to the board as you’ll benefit from denying space for units to appear out the other side.
From the wording the Wizard/Priest does not have to travel through the gate, it just has to be within 6" of the realmgate.
Yeah, at first I was being altruistic; thinking about my mates slower armies get around the board quicker, but then bastiladons etc popped in there. Nasty! Mwoo ha ha ha!