Setting up 457/401k Catchup plans to feed from single employee contribution amount

Using 12.2.10 OAB - I'm looking for a way to manage 457/401k plan contributions so the employee will enter a single rate and contributions will fill both the 457 and 457 Age 50 catchup buckets as needed, without the employee having to manage separate rates in self service. Is there a way to have the catchup plan setup where the employee just enters a single contribution amount, which is not exceeded on the check where the base limit is reached?  

We are public so use 457 plans, and currently there are 2 plans - the standard Deferred Comp 457 plan and the 457 Age 50 Catchup plan. The employee enrolls in catchup if they wish to participate and they need to manage their contributions amounts for both plans. The deductions are sequential so the catchup doesn't start until the regular annual limit is reached. Seeded functionality starts the catchup deductions on the check where the employee reaches the annual limit, but after employees got nearly double deducted on that check we added a custom skip rule on the element so that the catchup