I use the following knot sometimes for a tie off if I’m concerned a smaller knot will pull into the grommet (and I don’t have the option to replace the grommets, for whatever reason). Yulitle says in the video that this knot is for starting knots only. But if I recall, USRSA at some point recognized this knot as ok for a general tie off as well. I’ve never had a problem in the handful of cases I’ve used it as such:
If you want to stop the string from being pulled into the grommet you could get a 6/0 seed bead and string it on the anchor string when stringing. Then tie any knot you want above the seed bead to stop the knot from being pulled into the grommet. This will also protect new grommets from getting worn out deformed by the knots. The problem is if you have little room to begin with for a knot adding a seed bead will not work. Seed beads are like mini pony beads and about the size of a tie off grommet on the outside Just a thought I've never tried it and probably won't. You can get about 1,000 beads from WalMart of under $2.
EDIT: You could also put the seed bead on the tail end of the string you're tying off.