Applying SVG filter to background image

I am attempting to apply an SVG filter (Gaussian blur) to only a portion of an image (i.e. the background). I have achieved the effect by appending a clipped SVG image with Gaussian blur appli开发者_如何学JAVAed at the same position (to make it appear like the Gaussian blur is applied to the original image).

This is obviously inefficient and I'm looking for a better method. After reading some SVG docs and examples it looks like the enable-background attribute is needed but I would greatly appreciate some help on how to actually implement it!

Edit:

An example of the effect I'm looking for: http://img695.imageshack.us/img695/92/chromeblur.png

Here is a good description of how it should work in SVG

http://srufaculty.sru.edu/david.dailey/svg/SVGOpen2010/Filters2.htm

But SVG support is still incomplete in all common browsers. Especially the filter effects on backgrounds using the in="BackgroundImage" and enable-background attributes are not supported by any common browser.