My suggest : Add box-sizing support to PIE (for IE 6-7)
their is a .htc polyfill (https://github.com/Schepp/box-sizing-polyfill) and you can use it with PIE :
behavior: url('boxsizing.htc'), url('PIE.htc'); /*seam to works*/
but in some case they are conflictual (element is always resized on windows resize)
i think it was better to have this feature included in PIE.
Along these lines, something I've run into is that PIE always assumes that box-sizing is never set. Therefore, if you do set "box-sizing: border-box;" to your document so that widths are consistent among all browsers, elements end up larger in IE than in newer browsers.
Perhaps you could integrate the HTC code found here ;)
Couldn't you somehow set a special global state PIE.performReflow: false before you clear element.runtimeStyle.width, and then set it back to true when you are done?
+1 for this.