Nope. Gotta do it by hand. Blizzard disabled this kind of feature to stop people from setting up botting macros. If a skill in a macro triggers the global cooldown, you have to hit the macro several times to make all the skills go off.
However, if you want to consolidate those two actions into one button, you could use the macro:
/castsequence [reset=5] concussive shot, serpent sting
What that will do is cast conc first, and then if you hit it again within 5 seconds, it will cast serpent sting. If you don't hit it again within 5 seconds, it'll cast conc shot again. The number that reset is assigned to is how many seconds it takes to reset back to conc (in this case, 5 seconds), so you can raise, lower or even eliminate the reset as you like.