1) activate Fractalize "saw", leave amount to zero. Disadvantage: Fixed level of sub.
2) second PD wave? Could not figure out how to set the second wave one octave lower.
But how about the LFO? Yes, it's possible to use it as a sub oscillator.

Set LFO rate to 2.12.
To map the key to pitch I use the mapping generator.
C3 = 0, C4 = 20, C5 = 40 etc.
The level can be set by the Amp Mod knob.
Disadvantage of this method: LFO does not run @ audio rate, so it sounds dirty in the upper key range.
