Yep, that'll work fine. Make up the mix, and then chill it. If you put it in 2L bottles and use the carbonator cap, you can set the psi at 40 psi and shake it. I then disconnect the co2, shake some more, and give it another blast. Then shake some more. Within about 5 minutes, it's carbed up pretty well! You'll need a different carbonator cap for each bottle, unless you only made up 2L at a time. Since my kids are now grown up I only make 2L at a time. I forget the exact measurements, but it's 4:1 I believe so you'd use 1 cup of syrup to 4 cups of water.
I like doing it this way- first, no yeasty sediment in my soda and secondly, no root beer flavored beer line! I do have an old keg that I used for rootbeer years ago, and I never did get the flavor out of it.