How about in 13 months instead of 12? BJ fought at LW (Oct 2003), then WW (Jan 2004), then MW (Nov 2004). Just about 1 year.
his fight against Machida was actually @ HW
Rumble did 4 kinda
Brenneman WW Oct 1 2011
Vitor almost middleweight Jan 14 2012
Dave Branch 195 May 25 2012
Esteves Johnson LHW Aug 24 2012
Does Rumble count though? Pretty sure some of those he missed weight.