Does it vent to the outside in a place that would be suitable for an air intake? Could you place an inline blower somewhere along the ducting?

If the ducting is large enough and you can find or construct a register that would feed the MUA up around the perimeter of the range I am thinking you might have a really keen setup. User fritzp in the kitchen forum mentions adding a passive system with a motorized damper. He made his own cabinets and dadoed in registers in the back and sides of the rangetop. I wish there were pictures, but perhaps you could contact him through GW. The thread is here

Since the discharge is pressurized, I'd have to think that the input for a purely passive MUA system would have to be significantly larger than the outgoing duct in order to avoid negative pressure. Maybe Kas can offer some formulas?