Change My Pitch Up

I've been looking at programs that pitch shift the human voice while preserving the formants. The idea is to change the pitch but keep the vocal sounding natural - as though it came from a vocal tract.

In principle, I should be able to record myself singing in my own low baritone register, and then shift the sound up an octave or two into areas I can't reach, giving a female version of my voice. Ordinary pitch shifting would just make me sound like a chipmunk, but this should sound authentic.

Unfortunately, the programs I've tried so far - AV Voice Changer, Vox FX 202, Blaze Audio Voice Cloak and Phonotron 1 - don't seem very impressive. They either can't shift very far, or introduce flanging artifacts.

It's not like I want to sing an entire song as Shirley Bassey - though that might be, um, interesting. But a female choir singing chords in the background, or even a trio of female backing singers who come in for the chorus are nice options to have.
The computer we use to make DivXes of TV programmes has stopped working. Something to do with the connection between the power supply and the motherboard. While that's being sorted out we're using my backup system of freeview box and cheap capture card.
I'm pleased to annouce that I'm no longer living on tea, hobnobs and english breakfasts. It's now tea, custard creams and cheese sandwiches.
I've signed up to Tapegerm - a small online community of musicians who make tracks from each other's loops. Mainly because I think I can contribute loops that others wouldn't usually provide. The final part of the signing up process is to create a song from some loops provided - in effect, to show that you're genuine. I haven't shown that yet.