Can you be more specific in the porous medium? Are you just solving -k\nabla p = v and \nabla \cdot v= 0 there? Sounds like you can just split up in two subdomains. And define NS is one and Darcy in the other. You might not get exactly the correct boundary conditions if you use continuous elements though. What did you try so far?
You can read these on how to couple. The code is probably outdated, but the idea is the same: