Personally I would separate out your 5 main tanking skills from the locks damage.

so for example. Bind a key on the warrior that does nothing, but that triggers a castsequence macro on the warlock.

Then get into the habit of hitting the warlock attack key in between your 5 main tanking skills.

e.g

You have your 5 main skills bound to keys 1 to 5.

you would be pressing 1,2,3,4,5

I would suggest binding key 6 to nothing on your warrior but on the lock it triggers your cast sequence

e.g

(something like this - please not the conditions might not be spot on but you get the idea)

/castsequence [reset=24/target/dead] Curse of Agony, siphon life, corruption, immolate,life tap, drain life, drain life, shoot

or

/castsequence [reset=24/target/dead] Curse of Agony, siphon life, corruption, immolate,shadow bolt, shadow bolt, shadow bolt

You would then weave in your lock damage while tanking e.g

1,6,2,6,3,6,4,6,5,6

I'm sure it would become second nature after a while.