How can I add taxable income to a vendor that did not have a payment in 2015. They had invoices dat

How can I add taxable income to a vendor that did not have a payment in 2015.  They had invoices dated in 2015 but they were not paid until 2016.  The problem was one of our employees went to being an Independent Contractor.  The individual repsonsible for the invoice keyed the first 3 invoices to the employee supplier record.  They were paid in 2015.  How can I get that income on a 2015 1099?