Purely out of interest, what part of SE IR privileges allows you to operate an ME (CLT) aircraft if those IR privileges were gained on an SEP?
Don't know the answer, but I would suspect and hope the answer is "You Can't".
I would suggest that Appendix 8 Credits etc is where the reason would lie, in that if you hold an SE SP IR you are only credited that amount against the ME IR - now I know that is only for revalidation but....
Furthermore,
Applicants for an IR shall pass a skill test in accordance with Appendix 7 to this Part to demonstrate the ability to perform the relevant procedures and manoeuvres with a degree of competency appropriate to the privileges granted
Now, from my point of view... have you demonstrated the ability to maintain control of the ME CLT aircraft in IMC in the event of an engine failure - not just from a CONTROL point of view but from a PERFORMANCE aspect?
I would be worried that someone who has a ME Class on the Skymaster and SE IR on a SEP but not undergone the IR Test in the ME CLT could find themselves in a bad situation very quickly.