I use the same setup and im wondering why you need to cleanse at all on the pally?

i have 1 button bound for all the shammys which does

/targetparty

/castrandom Cure Poison,Cure Disease

I have this on 2 of the shammys and on the other 2 i have

/targetparty 1

/castrandom Cure Poison, Cure Disease

Putting the 1 there makes it cycles backwards through the party. I jsut spam this until everyone or whoever needs cleansing is done. Takes at most a couple of clicks. Which is only a second or two. I use to run with the pally using this as well which on his bar was

/targetparty

/cast Purify

I just became annoyed with having to reclick on the mob i wanted to attack. (I use focus) and then continuing on the dps macro which includes the assist.