You're right those planes have intake ducts. Outlet ducts would certainly be possible (since that what thrust vectors and reversers do) but may be less efficient for normal use. Like you said, they may not fix the pitch up issue either way.
Another option might be to mount the engine further back (in the "correct" position to avoid the need for MCAS), and have a duct for the upper part of the cold air stream immediately behind the main fan. The duct could redirect the cold air down the sides of the engine, under the wing, then emit it above the hot air stream behind the wing. This would allow the engine to be positioned higher up with part of the upper fan in front of the wing.