HTML......Dynamically populate a file

Hello All,

We have a situation in which we have to fill up a webform for many users [kind of a data entry project].We saved the html file from the customer's site and made some changes in the javascript so that most of the fields are filled by onLoad [the JS function].We already have the required data so its not a problem to get that in the html form.The issue comes on the  <input type="file">.We want the value to be taken up dynamically.Like onLoad the value populates in it.Right now we have to manually select the file and then hit submit which increases the time required to submit one form.
Please guide us on how can we dynamically fill up that part.....

PS: The names of the files we want to upload are all in a series ,for eg.  file 1,file 2 etc.....

Thanks