If I hear someone make a brocho after I have exited the bathroom before I washed hands, can I answer Amen after just cleaning my hands by rubbing them against my clothing?

Horav Shlomo Miller’s Shlit”a opinion is that you can. However, you must not only clean both sides of the hand but also the areas between the fingers. (It may just be faster, if the little available time permits, to pour some water on the hands).