I originally posted this on DSL Reports and I just thought I'd post here too for those who would like to try this.

Summary

DO THIS AT YOUR OWN RISK.
FLASHING CAN PERMANENTLY BRICK YOUR MODEM.
I ONLY DID THIS ONCE & CAN ONLY CONFIRM THIS WORKS WITH MY MODEM.

RENTED BELL MODEMS ARE BELL PROPERTY.
YOU MAY GET CHARGED FEES FOR MESSING WITH IT.