Then simply use singular they without changing plurality—so in place of your sentence you’d have Each employee must keep their laptop secure when storing it in their unattended hotel room.
English, both spoken and written, has been doing this for centuries. Why so many people are currently trying to make sure closely edited written prose doesn’t do it, I really don’t understand.
(And as for Ms, my wife consistently goes by that, and corrects people who use Mrs. with her. It’s not just useful for single women.)