Was playing with macros a bit.
The problem I have with one button macros is that movement, Hero, and the various procs mess them up.
Here is what I came up with that works for me... Its not a one button, but it lightens the load a fair bit by making sure Mind Blast and Mindbender are kept on CD.
/cast [nochanneling] mind flay
/cast mind blast
Manually apply Shadowword: Pain and Vamperic Touch, and then spam the macro until you need to refresh the dots.
Remember to fire off Devouring Plague when you have 3 orbs and Shadowword: Death when its active and you'll be all set.
I really like ShadowPriestDotTimer to help keep track of dots.