Pentatonic Diatonic Transposition?

[Daniel]

Hello,

I have recently discovered Lilypond, and wow. It is just great. I have been
looking for something like this for a long time.

I have a question on how to diatonically transpose a motive in a non-major or
minor scale in this case, a pentatonic.

For instance, suppose I have this pentatonic {a c d e g } and I have a phrase
that is {a c g e} and now I want that phrase to start on g so transposed
diatonically to the "mode" (its not really, but that is basically what I want)
of that a pentatonic it would be {g a e d}. 

If I use regular "\transpose a g {MyPhrase}" it will come out {g bes f d} and
include notes that are not in my original a minor pentatonic.

Can I define my own modes? I know that \dorian, \ionian are in there somewhere,
can I make my own scale\modes somehow and just use those?

Thanks for any advice or snippets!

Daniel