I would just deduct things like trade publications equally amount the properties. How is T&M involved? Going to real estate seminars? If so, I would also allocate equally amount all the properties. 

Back in the dark ages, I just carried an extra property to do these things, but the advent of PIGS and PALS put an end to that practice.  I recall things like pens & paper, PO BOX, postage, ....