This can be accomplished by employing an Outbound Campaign Manager, such as Acqueon, a S+ partner.

Acqueon has a solution for this.....Both Estimated Wait Time and Scheduled Callbacks can be enabled.  Keeps everything in house w/Cisco.  Acqueon Callback 

Acqueon (www.acqueon.com) has a courtesy callback/scheduled call back capability. Allows the caller to choose which option (hold place in queue or schedule a callback for later in the day/week).

With 8.5, it seems to be documented that non-ACD calls on a non-IPCC line can be tracked/reported on via UCCX Reporting.  Using the Agent Detail report, there is a field for Call Type.  This field seems to indicate what type of call/extension this is...