I heard an interview recently where Gardy referred to Mike Pelfrey as "Pelly." While I think "Stadium Emptier" is probably a more appropriate name for Pelfrey, "Pelly" seems to be a typical nickname construct from Gardenhire which is limited to taking the first sylable of the player's first or last name and adding a "y" (or "ie") at the end. Nick Punto was "Nicky," Justin Morneau was "Mornie" Aaron Hicks is "Hicksie", etc. This is the same nickname format used on Pee-Wee's Playhouse where the chair was "Chairry," the globe was "Globey," and the Pterodactyl was "Pterri."
I'm assuming this unimaginative nick-naming is largely influenced by Gardenhire's own unimaginative nickname of "Gardy". Perhaps if Gardenhire was known instead as "Da Doo Ron-Ron" or "Garden Gnome" the Twins clubhouse might be a little more colorful.
Johan Santana was "Jo-Jo." The possible reasons for this would be that under normal Gardy Playhouse convention, Santana would have been "Santy" or (phonetically) Yo-ey both of which are probably offputting to even Gardenhire. Whereas (phonetically) Yo-Yo would have been more acurate than Jo-Jo, calling your best pitcher in a generation Yo-Yo is probably not a prudent motivational move.
Joe Mauer and Joe Nathan are both just "Joe" to Gardy. (Although I think Nathan was "Nathan" more than "Joe" as Mauer seemed to be the one true "Joe" to Gardy While both names are simple, either one could have easily been a Jo-Jo, Mauer could have been "Mauersy" or "Mau-Mau" and Nathan could have been "Nate." There seems to be a level of deference Gardenhire grants a few players but I would have expected Morneau and Santana to be exempt as well. Morneau's a Canadian and Santana's a Venezuelan so perhaps Gardy's nickname exception also only pertains to American players.