Woolwings,
One thing no one mentioned to you is the ME(CRI) needs 30 hours of P1 Multi piston time for an FI(A), your multi crew turbine hours won't count.
However one thing you should look into is becoming a MPL (K2) was (j2) instructor, only an ATO running MPL courses can do this upgrade. What works in your favour is this requires 1500 hours of multi crew experience (which I assume you exceed by some margin) and an IRI, this will allow you to teach the basic and intermediate phase of the MPL course. It will be better paid than SEP instructing and you won't be competing with existing experienced SEP and MEP FI(A)s. Only drawback of course is at the moment everyone is waiting to see which airlines will be resuming MPL courses after the recent close down.