Fixed Fit-to-screen background on mobile web and web

I am looking to create an mobile web site with a background that is "fit-to-screen".

An example of what I mean by fit to screen is here:

www.launchrock.com

I also want the background to be fixed, so when the content scrolls (if scrollable) on the mobile device, then the background will not scroll with it.

any suggestions?

I will be using canvas elements, i have played with both javascript and css options but haven't figured out what works out the best as of yet.

i am sure you can find some java mobile scripts for viewing if the script your using does not have that all ready.

what do you have so far?

I'm working on my first mobile site (placed in a subdomain of the main site) so I'm not experienced with them at all yet.. but for the time being, I'm just using script in the header to call a different css depending on the browser size detected.

I'm sure I will find an easier way as I learn, but just thought I would mention it as a possible option