You could also use any tube from cardboard, rubber or plastic that fits your set-up.
I kept my lens attached within its retainer which has a threaded end, so I was able to simply stretch my tight fitting tube straight on without any glue. It looks like an extra camera control that you are simply fiddling with, which is good for candid shots. It can even stretch over the little lens for protection when not in use.
Simply hold the lens/rubber tube assembly between thumb and forefinger above the N.A. scope. No attachment is neccessary, and this gives you even more control of the magnification just in case you need that tiny bit extra.
Remember the film winding is loud with the T3 - unless you hold the shutter down. It only winds on once pressure is released.