PHP File upload redirect

Ok, this is might sound like a security hole but let's ignore that for a while. I need to allow users to upload a file to my website but I want to be in control of generating that file. I have a form where I want the user to create the new file and then that file should be the one that is up开发者_JS百科loaded. Is there anyway I can subvert the file upload control so that instead of popping up the 'Open' dialog box, it pops up my form and then when the form is submitted, the new created file is the one that's uploaded with the control?

Alternatively, I figure I could just use a regular button and a bit of JavaScript to open up my form in a window but then I would need a way to automatically the file to the form to be uploaded when my external form closes.

Thanks for the help!

If you want to be in control of generating that file, why not just have the form submit all of the information required to generate the control, and then generate the file on the server?