I came up with this, using 2/2 Crimson Scourge (Free Blood Boil when you refresh Blood Plague)

Spam Macro
/click Button1
/click Button2

Button 1
/castsequence reset=combat/target icy touch, plague strike, death strike, nil
/castsequence reset=combat heart strike, death strike, heart strike, icy touch, plague strike, blood boil

Button 2
/cast rune strike
/cast blood tap

If you specced into Epidemic (extend disease duration) you may want to add another heart strike, death strike, heart strike cycle