Self-Assess Tax in Payables using Use Tax rates as opposed to the Sales Tax rate setup in eBusiness

I was wondering if anyone could help me or point me to documentation that would assist.  We are implementing eBusiness Tax in Purchasing and Payables and have loaded sales tax rates in our system.  Tax is automatically calculating as expected in Purchasing and Payables.  We have a requirement for a few states where we have locations to self-asses the tax in the event the vendor does not charge the sales tax on the invoice.  However, we would like to have the system calculate tax using a Use Tax Rate when the user clicks on the 'Self-Assess' checkbox in AP rather