For Employer Match expense: The Employer would be posting the expense as offset to Liability, for purposes of the 2018 tax return for the business. Then, the Banking happens in 2019, to pay out that liability.

You cannot do this for employee deduction in the Wrong year. That isn't possible, by definition of "from paycheck" dates. The employee deduction is on a dated check, held as a liability to pay out later. You cannot deduct from 2019 payroll and call it a 2018 deduction.