Preferred Vendor

Hello - I am looking to automate the preferred vendor box on an item record. We currently have the multiple vendor feature turned on. We typically only use one vendor for most of our items. The issue I am having is that when creating an item record, under the vendor subtab, our employees are selecting a vendor, but then forgetting to check the preferred box. Is there a way to automate that so if there is a preferred vendor listed, the preferred box gets automatically checked?