There isn't really a great way to do that. Because MD triggers the GCD you cannot add it into a regular shot rotation.
I have an MD macro that casts MD on my focus target. You target your tank and type/focus to set them.
Code:
#showtooltip
/cast [target=focus] Misdirection
If you are having serious threat issues, you should be using Feign Death more. It will completely wipe aggro when you use it, and it's on a fairly short timer. You really shouldn't be having any threat issues as a hunter. Be aware of racial talents as well (Night Elf stealth, etc), and keep in mind that Disengage might help you kite if you pull until the tank can tag it back.