Had a look at this – and – nope – can’t find a way of doing this.
Maybe you could use stereo matrixes instead of mono, but just use one side of the routing. That way you can pan the send from the combined master to each of those busses. Is messy and wasteful of physical outputs and mix busses, but does get you kinda what you want?
BTW, have you noticed how the matrix sends seem to be POST FADE, but PRE the channel’s BALANCE/PAN. Means you have to set the balance/pan individually per send!? confused me for a minute why my master wasn’t panning. (I rarely take a feed straight to physical outputs from the master)