The reason I didn't hit deadline X? 5 "spontaneous collaborations" happened at my desk in 3 days. Wait... I don't get my bonus because we missed the deadline? But... my collaborations helped the marketing dept hit their goal ahead of time, and they did it by coming to my desk and asking me questions. Oh... that'a a different budget?
If you want to foster that sort of behavior, make sure all of the aspects of the business line up in support of it, not just the facilities budget because "open plan" is cheaper than private offices with doors.