I restored a pewter RL brush with a silvertip from TGN. The hole was quite a bit deeper than the base of the knot so I used a slice of synthetic "cork" from a wine bottle to "lift" the knot. It was exactly the same diameter as the base of the knot, which was convenient, and the two-pack epoxy I used is still holding everything together after 18 months usage.
Excellent reporting! That makes things so much easier. I should have assumed a pricey materiel like pewter would be hallow.