I believe you have to go out of Sonar and back in with a midi loopback. I just did this using loopBe, a virtual midi patchbay. One midi track with the midi clip sends its output to midi port 1 on loopBe. Then two other midi tracks take their input from this port, each with their own synth. Latency may be a problem. Sometimes it seems ok, sometimes not, but this may have to do with the samples I tried.