Contributions received for unenrolled individual with participating employer - Can we return [all] funds to employer?

[KaJay]

Background
Participating Employer-A of a 403(b)(9) non-electing [multiple-employer] church plan sent both EmployEE and employER contributions to the Plan for an individual who is not enrolled in our Plan under that employer. The funds came to the plan with remittance instructions while the employer and employee were working to get the employee enrolled under Employer-A. The Plan does not have an auto-enrollment provision but does require enrollment paperwork be processed before it accepts any contributions - for whatever reason, the employer sent the funds anyway. The employee has since decided not to enroll in the Plan under that employer. He is, however, enrolled in the same Plan under a different employer, Employer-B. Meaning, he works for two different participating employers.  

Question
If he is not enrolled in the Plan under Employer-A, are they even considered retirement plan contributions? What are the Plan's options from here? Employer-A wants us to send all the funds back to them. My understanding is we must keep A's employER contributions in the Plan which will be used to offset future employER contributions for its enrolled employees. We are unsure if the money sent to us as "pretax deferral contributions" should be distributed to the employee (per usual) or if some other type of arrangement could be made.