I once worked in a QC lab where we tested the acidity of organic esters to see if they had any free acid in them. The method was based on titration with strong base in methanol solution, using phenolphtalein.
To do this you would need an aqueous solution of sodium acetate or bicarbonate to get the phenolphthalein into its pink range, but I can tell you from experience that if you have a titration right at its endpoint, atmospheric CO2 and a bit of swirling is all it takes to turn the phenolphtalein back to colourless. Whether you can get the CO2 back out again by sucking with a syringe is another matter. Heating would help.
If you do it this way, you're going to need to change the experiment somewhat, but you should have something that will work. Here's a simple experiment (not exactly what you want but it uses the reagents I mentioned.) http://www.sciencegeek.net/Chemistry/chempdfs/QualitativeAnalysis.pdf
A great thing about phenolpthalein is that when it's in its colourless range it is absolutely colourless (due to the lack of conjugation in the molecule) so you can put lots in for dramatic effect. According to http://en.wikipedia.org/wiki/Phenolphthalein Phenolphtalein is used to test the curing of concrete by CO2, and the reaction and indicator are used in various toys.
Another thought: We used to add solid CO2 pellets to water with indicator in it for fun. That's certainly a way of getting a lot of CO2 into water. If I remember rightly the indicator was methyl orange. The colour changes only while the CO2 pellet is subliming. Once the pellet has completely disappeared, the colour changes back.