McDave, Instead of a paint can, use a standard galvanized bucket. Fill to 3/4 full with water and do the release. If you stay dry, you have a good release, if you are wet, your release is "all wet." :D
Part of the idea is that you can learn the FEEL of a totally relaxed string arm from hook to shoulder and how it helps the release. Then transfer that feeling to a drawn bow.
Arne