Thought this might help a lot of the one/two-man performing artists out there. I remember a thread where someone pointed out this boss octaves that only applied the FX to the lower strings. Much better for bass and guitar simultaneously.
In order to get a bass sound while I play guitar, I make use of the parallel path.
In the first stomp, I insert the transpose FX and set it to -12, which is one octave lower than the guitar tuning.
In the second stomp, I insert a graphical EQ. This is essential if you want to restrict the bass notes to your lower strings and not the higher ones.
In the graphic EQ, adjust the high cut to about 50-100 hz, depending on taste, this will reduce the transpose effect on your higher strings.
Adjust the various bands of the EQ to increase your bass response. I like to set my lower frequencies with a bit of a boost, while restricting the higher frequencies which are not essential to the "bass" sound.
Adjust the volume of the EQ to optimise the level vis-a-vis your guitar sound. You should use this in conjunction with with the parallel path blend, I set mine to -0.5, i.e. a bit more in favour of the bass sound so that it cuts through.
In conjunction with morphing, you can do some cool things, such as completely dial down the guitar, play a bass riff into the looper, then fade in the guitar again!
Hope this is of help to some of you out there!