How to use D9 as print fan with Mixing extruder? (no replies)

Hi there,

Just like the title says, how can I use D9 as print fan when using a mixing extruder? Because I use a mixing extruder I have to enable a 2nd extruder, but because it's an mixing extruder, there is only one hotend. Now I have D9 free for a print fan, but the software doesn't allow it, because I enabled an 2nd extruder.

Is it possible to change the firmware somewhere so I can use D9 as print fan?

Thank you in advance!