A method for forming honeycomb structures, such as wall-flow honeycomb filters, which utilizes extrusion of multiple material supplies at once. Such methods may be used to form intermittent plugs or other structures in the cell channels during the extrusion process, for example. A die assembly is provided which includes secondary feedholes machined in the pins for intermittently or periodically injecting secondary material (e.g., plug material) into the cell channels of the honeycomb structure while it is being extruded.