Laugh all you want... but,
According to Paul:
" set throttle proportional to PWM duty, and then limit max throttle to whatever level you wanted the max voltage to stop at."
Assuming that the accelerator pedal allows for a range of 0-100% throttle, physically limiting the accelerator (with a block of wood) to the maximum percent voltage you would want would work fine.
I would put that solution more under Yankee Cleverness than Redneck Engineering.
We do sometimes allow ourselves to make things more complicated than they have to be or think that there is only one way to "do things right".
In this case, doing the work in the electronics programming level sounds like the best way to go, but if you want to drive your EV like the kid at the beginning of INDIANA JONES AND THE TEMPLE OF DOOM, I won't stop you!
