Would it be possible to clear the passageways with music wire?
One of my co-workers a number of years ago printed a complex wind tunnel model with dozens of pressure tap passages running through it. However, as is common with SLS parts, many of the passages were blocked by layering and crumbs of cured nylon.
A piece of music wire of the appropriate diameter was sharpened into a chisel-like shape, chucked into a drill, then fed into the passages at slow speed, backing out frequently to clear chips and prevent the nylon from melting.
It took a while, but it worked. You must be sure, though, that the chosen music wire will indeed freely bend through the passages. Otherwise, it may well drill through at the first sharp bend.
Good luck!
Steve Hunter