From looking at the schematic: a typical gain control would be placed in the signal path after V1b to set the signal level to V1a. Other than the EQ this signal has no attenuation, deleting it might give you a bit more gain. You can see how much of a gain increase this would be by adjusting Treble, Bass and Rolloff for maximum volume-I doubt it will be much if any.
Alternatively you can try a different tube type, 12AX7 will give most gain, 5751 and 12AT7 somewhat less. Note that this will be at max gain and gain level will not be adjustable with simple tube swap. If max gain level is sufficient a gain pot could be installed...
My personal opinion and recommendation: follow advice given in previous posts and use a different pedal.