OpenERP - Store Expenses as Purchase Orders [on hold]

I've been looking around the forums and the internet in search for a solution to my problem but to no avail.

I would like to be able to press a button on the Expenses form on OpenERP when it is in the 'Paid' stage to store the data that is on the Expense form as a Purchase Order in the Purchase Order table with a sequential PO Number to boot.

I want to be able to press a button on the Expenses form which will generate the Expenses on the current form as Purchase Orders in the Purchase Order table, so I will be able to view these expenses as Purchase Orders effectively.

Is this too ambitious? Is so, how would I start? I'm guessing I would need to store the data from the Expenses table into the Purchase Orders table with the push of this button via an action/method.

I don't actually have any code to show as I'm not entirely sure how to start solving this problem, so apologies there.

Thanks to anyone who can help.