I have heard of people adding /stopcasting at the end in case you aren't on the instant cast of the exorcism/flash.

that way you only cast it if it's an instant. I haven't tried this myself... going to tonight.

you need to try to get Hammer of wrath into a sequence. I'm not 100% sure but I think it's not like other spells in that if the target isn't under 20% it won't cast or lock up your macro.

/castsquence hammer of wrath ,,,,,,,, < commas to match mash speed for 4 second cooldown