This can be accomplished in a gamified way: Game harness simulates people comming to an elevator, pressing destination button and waiting for some time (some wait longer, some wait shorter, should also depend on distance) before giving up and taking stairs. The elevator could or could not know about it's capacity. Assigning "price", optionally differentiated by input/output floors, to passenger, result would be €/time or €/level. Level - predetermined sequence of passengers.

Interesting thing here is that "price" does not have to depend on distance. Taking passengers travelling short distances might look cost effective, but that could have negative effect on number of people going to a 20th floor.