R. Waldenberg (Tzitz Eliezer vol. 6 p. 230) brings the opinion of R. Yehudah Navon that even according to Rambam there would not be even a rabbinic prohibition since physical contact, in this situation, can not lead to the illicit biblically forbidden act. But, it is nonetheless detestable to breach such limits and engage in physical contact despite it not leading to "uncovering nakedness". TE then argues that even according to opinions who would prohibit it on a rabbinic level would hold so when there is physical contact which is obviously prohibited.
Finally, TE concludes that such seclusion should be avoidable unless unavoidable and not left to others' suspicion.