Unfortunately, no one outside of Canon is able to provide such low level of support. 3rd parties depends either on standard protocol implementations or the existence of a suitable software developement kit provided by the manufacturers if they use proprietary protocols. It's the manufacturer's responsibility to provide system-level compatibility, usually through a special driver or software application. The PTP mode sort-of work because it's a standard and that Windows has "generic" support for PTP devices, so basic functions like file transfer works. For Mass Storage mode (where the camera appears like an external drive or USB key) the camera's firmware must identify itself in a way that makes Windows recognize it as an external mass storage device. I'm sorry to learn that this mode does not work with your camera on Windows 7.
I did a bit of research and found
this document on the Canon site, regarding Windows 7 compatibility. Your camera is listed as "requiring the Canon EOS Utility" and as "not
recognized
when
using
standard
function
of
OS", so I'm afraid there is no option other than want for Canon to provide the necessary support. The situation for 64-bit Windows is even worse: no support at all from what I've learned.
Windows 7 features a new mechanism providing an excellent level of integration with compatible devices (see
here for an example based on the Nikon D90). One can expect that Canon is working on a similar solution for its own cameras.