I have heard from subs who occasionally top their Dom to please hir, even though it doesn't work for them, by thinking of it as just another kind of service.

In passing, it's worth noting that even if you are beautifully compatible in your usual D/s roles, it might not work the other way. My late wife and I were a match as Master and slavegirl, but when we tried switching a few times, what we wanted from the scene was completely different and it just didn't work. Fortunately we were poly so had no trouble finding other people to satisfy our switch sides!