The VESC has most things present to achieve boost DC/DC and charging functions. Some controllers on the market feature this. One of the motor phases could be used as an inductor or even an external inductor could be used.
the way that it could work: disconnect a phase leads so you have access to the H-bridge
battery stays connected in the same way as if it were a motor controller.
on the the phase leads input your power supply(Ud) with caps (Cd) in parallel and inductor (L) in series. (referenced to BAT-)
Uo is the battery.
T1 is the bottom switch T2 is top switch