You seem to be adding a few unncessary steps in the process.
Why use a Document Library as the interrum respository? Just so you can use InfoPath? Why even have this two step process?
You can create a custom list to store the necessary information, with a custom content type, and implement an event receiver for the ItemAdding event. You don't even need an InfoPath form since SharePoint will provide a UI from your content type. The forms can be customized in SPD or
Custom SharePoint List Forms[
^]