I would like to bump this.
It would be very useful if this would be possible.

I realize this is a 6 year old thread, but this information may still help someone later down the line.

I've discovered a much better way of including your desktop capture into the multicorder. Go into the Output settings and under any of the actual "output" boxes (1-4), you can select the input number to be assigned to the output that you modify. After that, you can go into the multicorder settings and check the box for the associated output. This is particularly useful if you are only wanting to capture a specific window rather than the full desktop display. Also, it negates the need for the NDI feed to capture the output.