I do this on a regular basis, it is pretty awesome. You can also cut it with water or milk if its too strong for you, but I think the bitter coffee taste and the sweet of the chocolate go really well together.
OP- by "machine" at the office do you mean a vending machine or some countertop device? Yours sounds pretty fancy, so ymmv, but my experience with the former has been that no matter what way you mix it, it still tastes pretty shit.
Here's the starbucks coffee chart to explain some different mixes.