VA is weird.  We have both Subtractions and Deductions, each with their own set of codes.  You're looking for a Deduction (code 104) instead of a Subtraction.  ProSeries does a decent job of this and should keep track of carryovers per plan.  Don't feel bad, I had the same problem the first time I tried to do one of these, "but I don't need it to come out of the refund, it's already been done!"

If "Deduction" is not enough of a breadcrumb try drilling down into VA Sch ADJ Line 8 (I no longer use PS so don't remember exactly where to go).

Rick