Hi Alphonse,
I actually used the Groove Agent demo to test the latest 1.21 release that supports recording of plugin MIDI output. In the GA editor you need to go into edit mode, open the setup lid and enable MIDI Output. In Podium you should just assign the plugin to a track as you would normally, and then record enable the track and start recording. The GA works a little strange, in that you also have to press the Run button in the plugin. I also tested with the MicroTonic drum plugin which works a little smarter in syncing play/stop.
Note that you can only record the MIDI output. Streaming plugin MIDI output into other plugins is not supported yet.