A frozen ATPL is ATPL theory(14 exams) + CPL module + MEIR module + MCC. When you've done all that you will have a CPL/MEIR/MCC. When you reach the magic 1500 hours, to include 500 hours Multi Crew time, plus a few other bits and pieces, you will sit an ATPL skill's test on a Multi Crew aircraft and all being well you will unfreeze the ATPL.
You could however do the CPL theory exams(7 i believe) and then do an FI rating and you would be able to instruct for payment. To add an IR to that however you would need to do either the IR theory exams or the ATPL exams. If you did IR theory you would have a CPL/IR but you would not be able to fly Multi Crew, you would need to do ATPL theory.
In other words, if you plan on going Multi Crew at some point with the airlines, then you need to bite the bullet and do ATPL theory.
The is of course the new EASA proposals that will do away with CPl or ATPL theory for FI's. Back to the old days of PPL's teaching PPL's. But hats another subject all together.