The actors join a growing list of Season 5 guest stars, including Max Greenfield, Jennifer Love Hewitt and Dave Foley
Writers may be low on the Hollywood totem pole, but their tweets reign supreme
Amir Blumenfeld, David Burtka, Richard Riehle and Fred Melamed have also joined the cast of the Christmas-themed comedy
Will reunite on project with his "Reno 911!" co-creator Robert Ben Garant.