It should be possible to use two IR sensors by using the G30 S-2 option to set the tool offset by probing.
If you can guarantee that only one sensor will be triggered at a time, by parking the other head in a position at which its sensor will not be triggered, then you could connect both sensors in parallel to the Z probe connector and use a trigger threshold of 250 instead of 500.
Bear in mind that if the nozzles are not at the same height, you can't do ditto printing or mirror printing.
