callback application on OCS

[Boy]

Hi,
We need to develop simple callback application for compact call center (50 agents) all agents are blended Inbound/Outbound.
It’s clear to me how to register request, but how to call back? All agents usually  participate in Progressive/Predictive outbound campaign.  Callback campaign also must be Progressive/Predictive. As I understand from documentation, agent can’t participate in more than one Progressive/Predictive campaign.
Any Ideas how to solve this?
Does, anybody have developed callback  solutions on OCS? How you do this?
Thanx for any help