Hi,
You can try this javascript idea:
function funcAutofillUploadForm() {
var uploadctrl = document.getElementById('MainContent_fuControl');
var inputCtrl = uploadctrl.outerHTML;
}
Now, inputCtrl would hold something like:
<INPUT id=MainContent_fuControl type=file value=ertterth name=ctl00$MainContent$fuControl>
You just have to find a way to replace the value part with your path.