Is there a macro you can make that will have you go from your flying mount to zen flight BUT spamming it wont cause you to dismount from zen flight?
I would try /cast !Zen Flight
An exclamation point before the name of a toggle-able should prevent it from toggling off when pressed repeatedly, if I recall correctly. (That's assuming you have the auto-dismount while in flight option enabled)
this macro may not entirely do as you wished unless you just remove the final command /dismount but this lets you
1)free fall from mounts
2)zen flight while free falling
3)mount up when in zen flight being still and just throws your hands up if you spam on the go.
pardon my choice of random mounts
/cast [no mounted] !Zen Flight
/castrandom [flyable] Jade Cloud Serpent, Cenarion War Hippogryph, Black Drake
/castrandom [nomounted] Swift White Hawk
just remove /dismount and you will be able to do what you wanted.