That's because if you use them, you lose them all the time anyway. I was going to post the Scuncy thing too. Victor Wooten (my favorite bass player if you don't know who he is) uses them for just this purpose. My bass-playing friend does too sometimes. They seem to work really well. Plus you can move it easily and quickly, and "store" it by sliding it up past the nut for when you're not needing it. Easy access!!
All that said, shouldn't you work on your muting as part of tapping? I'm not trying to be a smart ass, because I've not even gotten that far in my playing yet (I suck).