I agree with Fl1ingfrog that you still have the rating in question (SE-IR) and are therefore still the holder of that rating. You are currently unable to exercise its privileges, but that doesn't change the fact that you have it and have demonstrated your competency in this area. As long as it hasn't lapsed for more than seven years, you should be good to go.
I would suggest visiting an ATO and discussing the options that they offer based on the current status of your rating and your requirements. Any training needed to get back up to speed with your SE-IR will most likely be covered by the flying that you will need to do for the ME-IR. You are of course aware that the 5 hours are a minimum, you may end up flying more than that. Once you get to the skill test, make sure to confirm with the examiner that he/she will be happy to cross-credit the ME-IR results towards the SE-IR part. I am not an IRI or IRE but from a user's standpoint, have noticed that the requirements needed to revalidate both can be different. At one point we had to incorporate an extra approach to cover all the requirements, but your examiner will be able to deal with this, just follow the instructions at the time...