Veteran journeyman will compete for backup spot behind new starter Jason Castro.
Three months of rest have healed the quad injury that kept Mauer on the bench in September.
Dick Bremer and Bert Blyleven remain primary team in the booth, but a quartet of former Twins will fill in occasionally.
The Twins will open camp in Fort Myers next month.
Twins "are getting a good one," Dodgers field coordinator says of latest addition to Molitor's staff