Ian,
Unless something has changed in the last couple of years (which I'm pretty sure it hasnt) then you'd still need to sit 13 exams (All 14 minus VFR comms) to be able to add an IR to your CPL and gain a FATPL.
If you only pass the IR exams and then add an IR to your CPL you will have a CPL/IR and NOT a Frozen ATPL, there is a BIG DIFFERENCE.
Without a FATPL, as stated above you cannot fly multicrew types.
The Rotary world seems to be different however....