Anyway, today I think I finally got it. Selecting the bound layer and choosing one of the Release commands (like Release Layer) seems like it should work but none of Release commands will release a layer bound by the Use Selected Bones For Flexi-Binding command. I did notice that if I selected a different group of bones, I could reassign Flexi-Binding to the new selection. Then, it finally dawned on me: deselect all of bones and then choose Use Selected Bones For Flex-Binding. The layer should now be completely released.
Briefly stated: Use Selected Bones for Flex-Binding with no bones selected means no specified bones will be used.
Duh, oh yeah.

That probably seems obvious to some users but for some reason it confounded me for the longest time. I'm just posting this info here in case it was confusing anybody else.
G.
P.S., If anybody has more info to add to this, please post as I don't think I have it quite all figured out yet.