I would take that a step furthur to require that the ones who are currently here illegally are either disqualified, or have to return to their home country and go to the end of the line. And whatever happened to checking immigrants for disease...you know, public safety and all that?
Please! That was the rationale for giving free hospital services to illegals - otherwise they might spread communicable diseases, etc. No matter what you come up with, the government can turn it into something weird. However, I think many states and counties are beginning to take a second look at this type of thing (Prop 200, for example), because it's hitting them so hard in the pocketbook.
I say treat them - and charge Mexico. And if (when) Mexico doesn't pay, deduct it from some of the trade or benefits Mexico gets and give the money to the state or county. Or make Mexico set up some kind of health-care fund in this country for dealing with its nationals.