Could one not just use a preprogrammed BLE module for VESC? I sometimes put these into boards when the ESC doesn’t have onboard BT:
They’re not exactly cheap, but they wire in via the usual UART port pins of TX/RX/+/Gd
I think the FOCer’s UART pins are mixed in, so you’d have to re-pin the JST, but it’s still just the regular ones, and should just work.