I think there are 2 ways of doing this:
a) renew your SEP every 2 years by test (probably around £500), then fly the Ikarus on your SEP. As you say, C42 hours don't count towards your SEP. You'll need to do some training in the C42 and get it signed off by a microlight instructor.
b) Obtain a NPPL(M). Involves training (typically at £130 an hour dual) and a test.
b) is probably more expensive in the short term, but cheaper over several years.
The plus with a) is that it would be easier to regain currency on an EASA aircraft should you wish to return to exercising your SEP rating on such.
I think the C42 is a great aircraft, I fly one purely for my own amusement but they are a bit limited by weather, especially in this part of the World!
TOO