Well, as Dorico does not currently allow us to hide cautionary clefs etc., I guess that individual flows are exactly the way to go here. Of course it’s a bit frustrating that this doesn’t work with xml import. [But adding flows is really quick and easy and and you can cut and paste the examples one by one. Shouldn’t take too long… hopefully.]
EDIT: I just remembered that there’s a ‘split flow’ command somewhere, I think in write mode. (I’m not in front of Dorico now.) Take a look, you might not even need to cut and paste anything.