Can a special accumulator be set up with a date formula?

We use a special accumulator code to track 401k eligible earnings which is set up for each appropriate earnings code. The issue we are having is that when a new person is hired they are not eligible for 401k until 30 days after their hire date. Is there a way to set up the special accumulator code with some type of formula to not accumulate earnings until after 30 days from the hire date?