I agree with LoneWolfMuskoka. I was going to suggest partnering with stores or restaurants to only sell Pepsi products. However as LoneWolfMuskoka points out, consumers might choose another Pepsi product, instead of Pepsi, itself. Therefore, that doesn't really solve your problem.
I think the key is to target loyal Pepsi drinkers or people who don't yet have a brand loyalty. This would make targeting youth a priority.
If you haven't read "Positioning: The Battle for Your Mind" by Al Ries and Jack Trout, you might want to give it a read. Also, you might want to read some of the books written by neuromarketers, as they are working to address issues just like this.