pdbreen can't wait to hear how it turns out.
The recipe I did above wasn't good at all. I bought cola and cream soda extracts and so far the recipes turn out pretty good.
We just the yeast method recipe from http://www.wikihow.com/Make-Cream-Soda
Easy instructions and we scaled it up to 2 Liters and used our beer brewing bottles:
4 Tablespoons of Penzys Spices Pure Vinalla Extract Single-Strength Alcohol 35%
1/4 teaspoon yeast
2 Quarts of water
Mix...