Spider-Man is going to need space to maneuver and Stiles is going to need space to be in the room without being right next to the kanima, so he picks out the nearest lecture hall and sets up an ash circle near the front of the room with a little bit of extra mountain ash on hand to complete the circle. This could still go, uh, bad, so he takes a moment to just take a deep breath before running out the door and calling out to Spider-Man. "Uh, I've got it over here! It's ready!"

Once Spider-Man's close enough to shout further instructions, he adds, "Don't smudge the line, and you might not want to be inside it when I activate it! I don't know what your deal is, but you might not get trapped with the kanima!" Just to be on the safe side. Spider-Man doesn't match any supernatural entity he's aware of (and yeah, he's looked), but that's no guarantee he's not bound by some magic rules.