I've got this macro although I can't get the modifier to work,
I basically want it to if a hold shift to mount me on the Kor'kron War Wolf even if i'm in a flying zone
#showtooltip
/use [flyable]Corrupted Fire Hawk
/use [swimming]Kor'kron War Wolf
/use [noflyable]Kor'kron War Wolf
/cast [modifer:shift]Kor'kron War Wolf
/script VehicleExit()
/dismount [mounted]