No can of worms at all any more; In the days of JAA (prior to EASA) the IMC(now the IR(R) at the time was a national CAA rating so it could not be credited towards a JAA IR.
Now that the Competency Based IR (CBIR) route is available which the IR(R) can be credited towards then it is definitely worth doing. The CBIR is a cheaper route to the full IR than the approved full time course.
I thought most schools that offer modular training for the IRs had switched to only offering the CBIR anyway.