I've just set up a click/castsequence macro for my SPriest as follows:

Spamming Macro
/click MultiBarBottomLeftButton4
/click MultiBarBottomLeftButton5

Button4 Macro
/castsequence [nochanneling] reset=combat/162 vampiric embrace,devouring plague,vampiric touch,mind blast,mind flay,shadow word: pain,shadowfiend,shadow word: death,null

Button5 Macro
/castsequence [nochanneling] reset=combat vampiric touch,mind blast,mind flay,mind flay,mind blast,mind flay,mind flay,devouring plague

What this allows me to do is make sure that Shadowfiend is being popped initially, and then again on every cooldown. The first macro is always attempted before the second one, and the reset allows the process to start over at exactly the right time (assuming I have the mana to reach the next Shadowfiend call ><)

I find this use of null and reset to be an elegant solution to the comma issue, as that can be largely dependent on the speed at which you are hammering that macro key.

What is interesting about this is if spells are equivalent on the two macros (ie. VT,MB,MF line up after the first few casts of the first macro) then the system interprets both macros as having executed and progresses both of them. So by the end of the Button4 macro, the Button5 macro is 3 casts in, but then cycles through that dps macro until the reset timer is finished on the first macro.