switchable input on boss t bone (need some help/input)

[FUZZZZzzzz]

hi guys!

i planning on building a boss t bone for a friend's bday

im using the alex frias' modded jordan bosstone design found here:
http://www.diystompboxes.com/smfforum/index.php?topic=70080.0

i only have a question. i bought a very nice enclosure for him. its a sixties toy metal racetrack
you can wind it up with a key and the cars will drive small rounds on the track.

i would like to put that feature into the desing so i had the idea of putting a piezo underneath to mix the ambient sound into the fuzz.
i was thinking about creating a switchable input: guitat or piezo... and maybe a blend knob to blend the ambient into the guitarsignal..

is a spdt switch enough or is this too much for the piezo.. talking bout feedback etc..

just hope you guys understand this..

thanks!