The green I-94W form asks about your address in the US and makes no provision nor gives any guidance for those in transit. However you should just write IN TRANSIT in the space provided for the address.
Physical clearance of customs neer seems to take very long, and often you can just walk through. It is Immigration that takes the time, and this is variable depending on how many flights have arrived just ahead of yours. Try and take seats as far towards the front of the aircraft as you can, and once out of the jetway consider running if there are many passengers ahead of you.
Some years ago there were two examples of how to fill an I-94W posted up on the wall in the approach to the Immigration desks at LAX-TBIT. One in English and one in Spanish. They had been produced by writing in thick pen on the normal form and then blowing this up to A0 size on a photocopier. One of the fields on the fom is City of Departure. The English example used London, the Spanish example used Guadalajara. The field for this city name was marked as 10 characters. You would think they might have chosen a better Mexican city name for their example .......