Using an external instrument as insert?

If I have an instrument as LV2 or VST, I can add it into a MIDI mixing strip and it will process incoming MIDI and output audio into the mix.

Now imagine I have a non-plugin instrument running in Jack, such as Bristol. I would like to send midi events to it as input and get the audio as output.

This would be the equivalent of an insert, except inserts work with inputs and outputs of the same type (midi to midi, audio to audio).

How do I get this done? Of course I can send the midi to the instrument using Jack routing then reinput the audio as a bus but this is awkward.

It is awkward and it is likely to remain that way.