Can't really offer the answer myself, but perhaps you could just build it to use an 18v power supply, then have a voltage-starve control like you see on a fair few fuzzes out there? Then theoretically you can just turn it down around halfway to get 9V, and all ways between.

I'm certainly no defining advice-giver, so this may or may not do the job, but could be an idea!

If not, it's a free bump for you!
Last edited by jaybals at May 13, 2013,
Yes that will work

If it were me I'd use a SPDT (three lug switch) and wire the middle lug to the 9V+ in on the vero board and the other lugs to the 9V and 18V nodes.