In other words I think you mean some kind of temporary filler for the vessels.
With chemical engineering ingenuity I don’t know why that could not be done. I’m thinking of the process by which filled cordial cherries (in chocolate) are commonly made. While the innards could be frozen before covering (and that is a common homemade process) the commercial solution is an enzyme that turns the solid innards to liquid within a reasonable time.
Well not filler for the vessels, but scaffolding with hollow coring. Ideally air and water and nutrient permeable scaffolding.
Hey, that’s bio stuff for you medical folks. Boiling acetone works for me to smooth out the striations on printed surfaces of PLA/ABS. (Some youtube vids on that.)
But that problem has been encountered and overcome — especially when having to create small tunnels/caverns in the printed object.