Modify him somehow in the Fallout 3 GECK (by, say, adding 1 cap to him) then save- a copy of his form will be stored in the .ESP.
Then open that ESP in Fallout3Edit, and change the master from Fallout3 to FalloutNV and save, then open it in the NV GECK and save it. Now you've got a copy of Butch updated to FalloutNV that you can put into your mod with NVEdit.