Here's the best thing you can do:

1. Buy borrow or boost a Digitech Whammy pedal (the newer version). They have 2 outputs: effect and clean.

2. Set it to an octave down. Run the clean to your guitar amp; run the dirty low to volume pedal, then to a bass amp, preferably with a decent eq so that you can filter it to taste.

3. Use the volume pedal to control which notes you want to hear "bassified." When you're ripping a killer Steve Vai solo you obviously don't want to hear the "bass" doubling all those notes, hammer-ons, pinch harmonics, divebombs, and flamenco fingerpicking that I'm sure you will be shreddin' on.

You can put a reverb/delay pedal between the volume pedal and the bass amp if you want to have a swelling, sustained bass sound, so it doesn't cut off sharply when you go down on the volume. In other words, say you're playing A-B-E on the guitar, and you want the bass to just do the E, you will step up the vol pedal on the E, then back it off for the other 2 chords and the delay will hold that E. It sounds complicated but is really easy and intuitive once you set this up.

Basically with the volume control (or a simple "cut" box like the ProCo Cough Drop that disconnects the signal) you will be stepping on it for the notes you want. Like those organ-style bass pedal things, minus having to hit the right note.

The simple version would be just WhammydirtyOut---Bass Amp/ WhammycleanOut---Guitar Amp. The retardedly simple would be using the Interval function on the new Whammy, where you can set the pedal to play BOTH your original note PLUS the octave down. You can even set it to play a Fifth down or just about any other interval down, plus your clean tone. You'll have less tonal control cuz it will all go to the same amp.