There is a draw3dmouse function in the code archives. It would probably be useful if you adjusted it slightly so that it displayed other quads as well as the cursor. It uses a second camera so supposedly the zoom doesn't affect it.
http://www.blitzbasic.com/codearcs/codearcs.php?code=865
http://www.blitzbasic.com/codearcs/codearcs.php?code=865