i completely agree with the whole soda water and shots of syrup idea.
Does a number of things for you:
1. Saves your beer lines
2. Keeps your faucet from getting sticky and flavored
3. Allows the soda drinker to mix exactly how they like it
I always like my pop a bit watered down. I might use half the syrup an average 12 can/day soda drinker might use and we can both be happy with that setup.
Not to mention you can have 12 different flavors at once with just one soda water keg!
EDIT: You can also have this setup perfect for those who would rather drink alchopops than a beer. Hard lemonade? Two shots hard lemonade syrup, ice, top with soda water and viola! And the kiddies can have a grape soda right after!
Check
here for the pumps. You could just use the quikpour tops too like you would have on liquor bottles behind a bar.