How to setup a voluntary deduction that is a percent of gross not to exceed a flat amount per pay pe

We received a union deduction that states:

Union fees are currently 2% of pay per employee; to include a cap beyond which dues no longer needs to be collected, of $11.54 per week.

This is a bi-weekly payroll, so the limit should be $23.08 per pay period.

We setup a deduction element for the 2% of gross, however, how can we setup the $23.08 per pay period limit?

Thanks,

Andrea