just do a simple CPL, MULTI/IR conversion !!!!
no such thing, i'm afraid. taking your scenario for a like for like conversion. first, for the IR, there is a minimum of 15 hours instruction, plus a skill test fee, and aircraft hire for the test. the CPL is training as required, plus another skills test and aircraft hire. and don't forget the multi engine class rating, which could be as simple as just a test (plus fee of course), or if the CAA are being picky, the full course.
This should give them their JAA ATPL Unfrozen as far as i know
not true. the JAR ATPL is issued after completing all the pre-requisites (1500 hours, 500 multi crew, blah, blah) and passing an ATPL skills test. it turns out most people do this test as part of the normal OPC/LPC requirements of their company.
no short cuts in JAA-land, keeps the riff-raff out.