You can mess with the R6/C5 and the R7/C6 section with the Ruetz trimmer to modify the bass response, but if you scour the internet about that section on the circuit you will find that it is very much as double edge sword, in that it alters the traditional tone of the pedal. If you want the classic sound but straight up need more bass, the only way to really do this is to blend in some of the clean guitar signal.
The Buff N’ Blend mentioned above by Barry is the ticket to do this. You can basically use the buff n blend to make any of the gain pedals “bass guitar ready”.