Also, thin-walled lattice supports can be left in place with minimized obstruction of fluid flow. Though I would not trust any automated lattice fill tools, model the features fully yourself. Align them with the ideal flow direction you want to impose. Oh, and taper the entry/exit edges to reduce flow influence.

Presumably, you can get access in some areas to break off the supports. Can you increase access by integrating holes and bonded plugs to open up the most difficult areas?

Also, for supports that you are able to break off, you can design them with small, multipoint tapered contact dots or local necking to allow gentle break off and ease cleanup.

Finally, be strategic about placing supports – keep them away from flow-critical zones to reduce any downside flow influence you’re stuck with.

Oh, and I suggest you design all your supports into your model, rather than trusting any automated support structures the printer layout software imposes in the build. No software-built supports can ever have the understanding of the fluid mechanics of the real-use context you’ve got!

It’d be great to see what direction this takes if you could share some details later.