different rental price based on number of tenants in unit?

Our Denver 1/1 is an all-utilities-included unit because there's a single meter on our duplex.  Since those utility costs go up if there is a couple in the unit vs. a single person is there a way to charge accordingly?  or can you not have separate pricing based on 1 occupant vs. 2 occupants (which wold be our max with a 1/1).  thoughts on tackling this?  Thanks!