Have you tried donut wads under the balls that fit through the chokes?
Donut wads should keep the undersize ball centered in the bore and the wad will squeeze through the choke.
BPI has felt donut wads.
Having said that, I have not tried it myself but it is old technology that supposedly works.
I'd use an all hard card wad column with the donut wad on top then RB nestled in the donut hole.
I think cushion leg wads do not provide a stable launch platform.
Longbow