As Bandit said, check valve would prevent any siphon problem. If you wanted to make something to hang the 2 liter bottle from the side of your tank, you could probably use a wire hanger. Maybe put a sponge under the hook part, so as not to scratch or mess up tank rim. Then just bend the bottom part into some form of a loop, similar to those wire things used when dyeing easter eggs. May look a little ghetto though, just hanging out on side of tank. Nice tank btw, looks good, I also have a Emperor 280 filter, does a good job for me.
Also another option, if you don't want to do the DIY CO2, you could try Flourish Excel. It's basically liquid CO2, and helps as an algaecide. Look it up here on the forums. Many swear by it. Good luck.