Your only option is to upgrade or use the DNG convertor.
Just to be perfectly accurate, that would be two options.
To use the free Adobe DNG converter, you would download and install the very latest version then whenever you want to edit raw images you'll go through a process something like this:
1. Upload the .cr2 files from your camera into a folder on your hard drive.
2. Run the DNG Converter application and select the folder (it works on folders, not files).
3. Convert all the .cr2 files to .dng files.
4. Open the .dng files into Photoshop CS4 through the Camera Raw dialog.