Way to remove the uniform from the Spy without “being spotted”

I'm replaying the classic Commandos: Beyond the Call of Duty.

While playing the game, on the second tutorial mission, on the very beginning, you can use the Spy to stun a soldier and get his uniform. With this done, you can get to where the other ally soldiers are, but when using a uniform, the Spy can't crouch or pass the obstacle course and go to where the other soldiers are.

I want to remove the disguise from the Spy to allow him to crouch and deal with the enemies behind the obstacle course non-lethally, but there seems to be no way to do it, as there's no icon or key shortcut that I know of to do it and I haven't found anything on the Internet.

The only way I know to remove the disguise is by being detected by enemies, which automatically removes the disguise, but I don't want to be detected by enemies, of course.