When there's parts and assembly needed, I don't think that's only academic.
An inductor and flyback diode would do? I'd have to cookbook... whut's a fly-back di-ode? Wiki-time!
Oh... right, so the inductor can cycle the current from its own field collapsing.
How does Peltier efficiency with PWM compare to efficiency of a linear PS?
Suppose you used much lower pulse frequencies, into seconds per cycle like microwave ovens do?