SDK: ExtJS 4.1.1a

In my app.css I have image paths that look like so:

U:\apps\metrics_v2_extjs\resources\sass\default/../../../ext/resources/themes/images/default/box/corners.gif
I'm sure this is a result of using a mapped network drive (I have no other choice). Is there anyway I can define what my css image path should be as opposed to the build process trying to figure it out?