External Instrument track: parameters not assignable for QC

I created an External Instrument for my external MIDI synth and added some parameters in order to be able to use Quick Controls for an easy access to some of them.
When I add an external instrument track, the list of controllable parameters in the Quick Control list does not show the parameters I have defined, only the default controls are listed. BUT, if I add a MIDI track and set its output to that same midi device, the parameters do appear in the QC list. Is it by design like this? I mean it kind of defeats the purpose of simplified Instrument track when additional tracks are needed for controlling.
Is there a way to make the parameters assignable for QC on an external instrument track?