What air attachment screws onto a Presta valve with the core removed? High volume for seating bead?
Inflator heads with Presta fittings let you do this because they tend to (always?) seal down around the stem, not the core. I don't know any other way. I suppose you could also take a spare Presta core from a dead tube, break the plunger out of it to get more airflow, then temporarily install it in your tubeless valves and put your adapter on that. This is conjecture.

If you haven't already, one thing you might try if seating the beads with your inflator head plus an adapter just isn't working is first install the tire with a tube, seat the bead that way, then break just one of the beads free and try to do the tubeless seating. This can make obstinate ones go pretty smooth.