For those having trouble with the exclusivity and wishing to replicate pre-Page 2 functionality, you can do the following macros:
/macroimage "flight_combatflight.png" "Hover" "powexec_toggleoff Fly$$powexec_name Hover"
/macroimage "flight_travelflight.png" "Fly" "powexec_toggleoff Hover$$powexec_name Fly"
Those will look and work like the old Hover/Fly; however, you will not get the swirling icon to indicate the toggle is active (a limitation of macros). If this is an issue, you can use a keybind instead. I don't know what keys you use, so I'll use an example of "H" for hover and "F" for fly.
/bind h "powexec_toggleoff Fly$$powexec_name Hover"
/bind f "powexec_toggleoff Hover$$powexec_name Fly"
UberGuy already showed the bind solution, so I apologize for my redundant post.