Hello Simon,
depending on what make of system you have got, it probably has the emulators built into the lpg ecu seeing as it is multipoint.
If it's a Prins system then it should have seperate emulators, but most others are internal to the ecu.The easiest way ,although it is still a pain on these engines, is to remove the lpg cut harness connectors & put the petrol injector connections back as they were originally. You may find though that it doesn't have the cut harnesses & may just be wired into the switch side of each injector.
Hope this helps, regards,Andrew