you could use this:
#showtooltip Death coil
/cast [nomodifier] shadow bolt
/stopmacro [nomodifier:shift]
/cast [modifier=shift] Death coil

use the red "?" icon and on your action bar it'll show up with the deathcoil icon, including the cooldown.
just click to cast shadowbolt, and hold down shift to cast deathcoil. You can change the shifts in the macro to ctrl, alt, and i'm pretty sure something for right and middle click. I don't know them, but you could find them somewhere. Hope this helps!