[ffn]

Honestly, the best route IMO is to actually maintain an open-source portfolio of work. This obviously isn't feasible or possible for everybody, but if you can contribute to OSS, doing so is easily the best way continuously test your mettle and prove to your future employers, partners, and the general community that you're someone they want to (or don't want to) work with.

The true value of the face-to-face interview really should be getting a feel for the person - is this person someone I want to work with? Or will this person make me want to kill myself whenever I step into the office? - not to gauge technical prowess or whiteboard prove-you-are-smart-and-took-an-algo-class-in-college challenges