I am a tech lover, web/graphics designer and what I would do is a simple HTML. This page would have the coords listed on it so after they hit the QR code it will open their browser and the webpage that I made with the coordinates will show up. They then enter that into their GPS and proceed to the cache. OR you can link the QR code to the GPS coordinates through Google Maps.
The first idea is simple and will work as I have tested it. I have my own server and everything tested fine. The second should also work but may cross lines of Google so not sure if you need an API key or not to proceed with that one.
I LOVE THIS IDEA!
Aaron