I wonder if you could run the output from a piezo through say a 1:2 home-rolled transfomer and swap current for a higher voltage? Might be possible to get a generic (ie., cheap) piezo to work better in a high mix hybrid.
Or possibly charge a capacitor in the same sense? Impractical to an extent, but it would eliminate the need for a battery...
Throw that big chunk of piezo from the empire state building, when it hits the ground theres one hell of a lightning strike.
Well maybe not that dramatic, but whats stopping someone from taking it large scale and making some crazy arcs? (besides acquiring the material)