Not sure how you had it set up on the Novatouch, but usually I hear about o-rings on the Novatouch being on the keycaps to dampen the down stroke. In case it's unclear, most Topre silencing mods (dental bands, soft landing pads) are installed on the sliders themselves, at the base, to damped the upstroke. It works wonders.
The biggest difference between the o-rings you'd use on keycaps and the dental bands, I believe, is thickness. The dental bands are quite thin when installed and barely impact key travel distance. I hardly noticed a difference in feel even when I first installed them, now I can't tell. But the sound is much closer to the bassy, clean thock we like to hear out of the Topre switches. I recommend it highly as a cheaper (and easier) alternative to EK's soft landing pads (less ironing). I would not recommend using o-rings, as I suspect they are thick enough to shorten the key throw more than I would like.