Yes it is almost impossible, but...
If it is an MD110 (as probably it is), we made a solution, maybe it can help you too. All calls to the selected extensions are routed through a "thromboned" Q-SIG route to an IVR, made with the Envox platform. In Envox you can record the conversations. With external incoming calls this works fine, and this was the requirement for us. For outgoing external calls it is O.K. too. The problem is with the internal calls, how to route them through this thromboned route.