Had a session the other day where the client had the drummer do a second pass to play on top of the first part... with a two drummer sound in mind. Not sure yet if this second part will be used or not. It does beg the question though as to how one might approach panning.
 
Any thoughts?

listen to any classic '2-drummer' bands,
and see how they were mixed

List of double drumming bands[edit]

• ZARD (Izumi Sakai)
• King Crimson, 1972-1973, 1994-1997 and 2008
• Grateful Dead, 1967-1971, 1974-1995
• The Allman Brothers Band
• Bon Iver
• Bright Eyes
• Gorillaz 2010 Tour
• The Doobie Brothers
• Slipknot
• ...And You Will Know Us by the Trail of Dead
• Genesis
• Adam and the Ants
• Gary Glitter
• Modest Mouse
• Angels of Light
• The Melvins
• Frank Zappa
• Tortoise
• Hidden Orchestra
• Hollywood undead
• Dananananaykroyd
• Kylesa
• Ill Niño
• Godsmack, occasionally
• Do Make Say Think
• Pink Floyd, The Wall Tour
• Mushroomhead
• Black Eyes
• U.S. Christmas
• The Fall 1981-1984, 1993-1997 (occasional), 2014-
• NoMeansNo 1993-1997
• Radiohead
• The Roots
• Pavement
• Arcade Fire
• Levon Helm during the '80s
• Fugazi beginning in the early 2000s
• White Rabbits
• The Dirtbombs
• The Party Boys
• The Feelies
• Butthole Surfers 1983-1985, 1986-1989, 2009
• Bloc Party
• Course of Empire
• Combichrist
• Poliça
• Nick Cave and the Bad Seeds since 1994
• Tedeschi Trucks Band
• Joe Bonamassa
• Joe Walsh
• The Go! Team
• Cult of Luna
• James Brown
• Vinegar Joe
• Ministry during tourings 1989-1990
• Taraf de Haïdouks, a Romanian band
• Foreigner
• Big Pig
• Apollo 440 stop the rock
• Danielson
• Ringo Starr's All Starr Band
• Demetrius Williams and Malachi Burgess, double drummers for DPB Band and with Brian Haas of JFJO and others
• NEEDTOBREATHE

To me it depends on what the drummer did the second time around.   Assuming the second recording is used, if the drummer played the same part twice then I would sum each recording to mono and pan the mono tracks left and right similar to the way two recorded rhythm guitar parts would be.  If the drummer did additional tom fills, cymbal crashes or fancy high hat hits, I would treat the second recording as a percussion track instead of a drum track by using it as desired and placing the sound in a variety of panned locations throughout the length of the song.