Judging by the lack of response to this question, I rather think I may have committed (unknowingly)a terrible gaffe - perhaps admitting to owning a PME 90 is rather like asking the National Farmers Union whether there are any members who have carnal desires relating to sheep! I withdraw the question and apologize unreservedly.
The eyepiece of the PME is bigger than that of the PM90, so the thing will not fit.
Neither of the two available eyepiece magnifiers will fit the PME90. You will have to do with the PME90's eyepiece as it is.