Link Period End Date to Invoice Date in Invoice Preparation

I am trying to link the Period End Date (ProcParam.PeriodEndDate) to the Invoice Date (ProcParam.InvoiceDate) during Invoice Preparation. What I would like to do is when the user selects the Period End Date, it will automatically place that same date in the Invoice Date field. I have tried to adjust the field through the Extended Properties with no luck at all. We are on Can anyone help?