If you want to make a syrup, why not add something with sugar to it, to make it a real syrup?
I don't know how barefoot makes his stuf. But if i was trying to do something sort of like barefoot's; i would make a tincture of the wormwood and then make a real syrup with some kind of sugar base with the wormwood. And then i would mix the tincture and the syrup together. What you are trying to to do I have never heard anyone do before, so if you go with your plan you will most likely have to guess and mess around untill you get it the way you want it.
Good luck! let us know what you end up doing and how it turns out.