Steve - Thanks for the really, really detailed reply. But I don't think I need the info anymore. Here's why...
To begin, I didn't mention specifically "why" I wanted the Tenderfoot(s) off, because I was concerned it would lead too far away from the subject of how to get them off. But since you mentioned putting them under a maple block is not recommended, I'll elaborate.
I've got a low mass, rigid turntable on a wooden stand that I wanted to be both insulated from floor based vibration, and also from airborne. I thought a maple block, with Tenderfoot(s) between it and the stand would deal with the floor based vibration, and replacing the TT's stock, semi-soft, decoupling feet with rigid cones to allow vibration to "drain" to the maple, and would accomplish my goals. I bought the block, and got the Tenderfoot(s), but have not yet purchased the rigid cones. But I tested the maple block on Tenderfoot(s), on the stand, with the TT's stock de-coupling feet on top of the block. The result was some sort of crazy, low bass, feedback loop that made the TT unplayable, lest the cartridge go bouncing all over the LP. So, rather than testing again with my intended cones replacing the stock TT feet, I decided to remove the Tenderfoot(s) first. And the result has been excellent.
Since the Grungebusters remained on the maple block when I removed the Tenderfoot(s), I tried it. Now the setup is TT on stock, semi-soft decoupling feet, sitting on the maple block, with Grungebusters between the block and the wooded stand. And it is providing MUCH more isolation from floor based vibration than I expected. Much more than the TT just sitting on the stand (on the stock feet), and much more than the TT on the maple block on the stand. Inserting your Grungebusters between the stand and the maple block took out much more vibration than I expected. I'm honestly shocked that such a thin little layer can make so much of a difference.
AND I took the Tenderfoot(s), sans Grungebusters, and re-purposed them as replacement feet for my CD player.
So all's well that ends well.
Thanks very much for the help! And please let me know if I can anwer any more questions.