Cheap Trick No 3There is a simpler way, for years I have glued two lens back-caps together back-to-back to achieve exactly the same thing.
Canon Extension Tube EF 25mm II
Ok, not cheap in fact expensive as you can get 3 non Name rings for the price of this Piece of sh*te but...
This ring or any other Extension ring saves you real espace in your camera bag.
I always like to cary my lenses upright in the bag unless I go above 135mm.
The Problem are all this short stumpy lenses which are just 6 cm (or less) high but take up a full slot in the bag. Solution is to use the Extension ring to stack otherwise unstackable things together. My prefered camera bags can hold and protect lenses up to 18 cm long. So here is my EF 50mm ==> EF 25 II ==> EF1.4x stack