Just do your JAA commercial pilot licence conversion on a single engine. Do your JAA IR conversion on a multi. Then you have multi IR RATING on a Commercial pilot licence that you have just completed on a single engine aircraft( probably be a beechraft sierra or a Piper Arrow).
To sum up.
You will have a commercial pilot licence with a single engine rating on it, a multi engine rating on it, and a multi instrument rating on it.
Job done. In the most cost effective way.