Internal 7V-9V-12V voltage switching circuit ala Boss TB2W?

[Bandwagonesque]

Anyone know of a circuit out there that can internally switch from 7V to 9V to 12V while being powered by 9VDC voltage ala the Boss TB2W Tonebender? Wanting to build a tonebender MKII next weekend for a friend who missed out on those and was wanting to implement that if I could. Can someone point me in the direction of where I need to go to get started making this happen? Thanks everyone and hope you all had a great weekend

[iainpunk]

maybe build a simple charge pump circuit, and use a voltage follower opamp and a potentiometer to regulate from 18 to 0 volts, or use resistors on either side to limit the voltages.

cheers