Including 401(k) Catch-up deduction amount with-in Base 401k element

Summary:

We have a requirement that client doesn't want to show separate Catch-up component as part of 401(k) deduction, however they want to ensure that all eligible employees who are over the age of 50 to be considered for the deduction as IRIS limit under the base 401k element itself.
If anyone has come across similar requirements, can you please share details on the approach followed.

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