LPF cuts highs. you'd just get a mush of a sound... I'd suggest a blender pedal!
or even better - get the green russian muff. when i tried it, I didn't think it needed any pedal to help it (at least at low gain settings, which I usually prefer on a fuzz... + i never tried it in a band, it could suck... my Little Big Muff didn't work all that well in a band...)
what could maybe work was if you put an LPF in a blend pedal (or Boss LS-2, set to A+B mode). then, you can add top end back to your signal as well... I sometimes do that with my AF-9, set to LP and cut sensitivity and peak. it acts like a static LPF. when I blend clean signal to it, I get some weird kind of a smiley-EQ sound.