Is there a way to programatically create a "PostedFile"?

I currently have an HTTPINPUTFILE control on my page, however, is there a way to either write a value into this control using javascript (ie: some variable), then when posting the form, the file (which would be a something like c:\Test.txt) that was programatically entered into the control, be posted? Or is there a way to do this without using the actual control itself.

Any ideas would be great

Thanks in advance