I think you can modify the "shadow meld" skill or use dummy units to cast.
dummy unit for cast it is bad ideea, i tryed and bad when u get delay (needa short time for order the dummy unit for cast ability on u)
example u cast ability but during dummy unit cast on u the invisibility u can reicive attack and u get invisibility too
more easier to add permanent invisibilioty and if attack/cast then remove from him or just wind walk if no problem the icon
my ideea is combatstat system with permanent invisibility
(combat stat system need a damage detection system or atleast attack trigger with linked list timer)