Best approach to renaming(custom) file on upload

Hello - I need to rename a file as it's uploaded and want to do it with some custom fields (GUID and user name collected from a form). I'm not sure where to touch the code the lightest to get this going. It seems like one could possible add a parameter to this object or pass the WA_DFP_UploadFiles function another parameter, but I can't tell from the code in helperphp what the offsets are coming in for items like renameFileTo to test it out.

Any suggestions?

Thanks!

WA_UploadResult1_Params["WA_UploadResult2_1"] = array(
'UploadFolder' => "../../../admin/exhibits/horizon/images/",
'FileName' => "[FileName]",
'DefaultFileName' => "TEST",
'RenameFileTo' => "TEST",
'ResizeType' => "1",
'ResizeWidth' => "1024",
'ResizeHeight' => "1024",
'ResizeFillColor' => "#FFFFFF" );

WA_DFP_UploadFiles("WA_UploadResult2", "e1_img2", "2", "[NewFileName]_[Increment]", "JPG:100", $WA_UploadResult2_Params, "_Entry_1_2");