I've not tried them, but the Beman Classic MFX 500s are super heavy as is and with the addition of a brass HIT insert (75 grains) and 125 grain tip will get you into that 9+ grains per pound range easily.

Muzzy also makes brass inserts (50 or 100 grain) for standard sized carbon arrows (GT, CX, ICS, etc)- One of the trad guys who shoots at my shop isusing these in Beman ICS Hunter Camos out of his Widow and loves them- though he does shoot POC too.

3Rivers archery also sells weight tubes for standard sized carbons.

Yes I've been secretly researching all this stuff.