This is the route I plan on.
You can use your IR(R) and accumulated IFR flying hours towards it. You then do the CBIR training and take the skills test, how long it takes to get to that level will determine how long it takes and how much it costs I suppose. I am currently looking into ways to make my IFR hour building as beneficial as possible for this reason.
If you have the ATPL exams then it is an IR no different to any other.