I confess that I have found workarounds for pretty much everything in Dorico! But it does take a little bit of fiddling… If you have say a Sustain in one instrument and Staccato in another, load them both in the same channel, but then assign the volume knob (or any other volume controller) to say CC20 and the second instrument to CC21. Then in the expression map tell Dorico (add control change) that when playing sustain it must use CC20 at 100 and CC21 at 0 and then do the exact opposite for the staccato. This is how I work with the EW Choirs which have all the patches in different instrument/players.