This builds upon the clown car tecnique put forth by Estelle and Smashing Magazine.
Just other media queries (max-width, min-width, etc) it's possible to use -webkit-max/max-device-pixel-ratio and min/max-resolution to make the SVG 'retina' aware.
See the hard-coded demo page for a very simple example. The included php page uses a few helper functions to make outputting the URLencoded data-uri easier to mainuplate in development.