The University of Wisconsin refuses to pay anyone more than 100% of
his/her contracted salary--the accounting program refuses to print the
paycheck!  Yes, there are provisions for overloads, but one must jump
through lots of hoops.  Your case (translated into Wisconsin's terms)
would mean a 70% overload, for which there would be absolutely no
possibility of receiving permission.

I would try calling attention to this person's contract: 'look, it says here
you will receive x amount per year; if you are on sabbatical, you are still
an employee of the institution, that's what you get.'  If that doesn't work,
let his/her dean or vice chancellor explain it in more forceful terms.

Bill Campbell
Director, Grants & Research
UW-River Falls