Poking at an idea for weeks -- how to get two characters into a trap that is meant for one of them, that transports them elsewhere -- and finally went duh. It doesn't need, overall, to be targetted at one character.
So I had yet another character, a teacher, jovially explain the festive time, with its break down of rules, at a liminal time. (LIminal time being important to their studies, so they will need to know all about its significance of transitition.) And there are enchantments that mirthfully go off at odd times.
As long as the transport spell has a special trigger for the situation where the targeted student goes in, it works. Well, as long as it can accidentally sweep along the other. Then I can work out a reason for the villain of the piece to be careless about it. . . . hmm. . . .