Wait, found it for the non-phone API. Again, I don't know if requesting an unlock nets you the standard pin/password prompt.
There's a workaround for calling other apps, which might net you the ability to send an email or post to facebook or something, but those other apps would have to already declare they can handle whatever it is. That is, still no starting completely arbitrary applications, and you don't actually get to pick it (managed by user, sometimes at each call). I have no clue how this would interact with the lock screen, if it'd even be allowed.