The issue is that aegis won't grant you access to mceeviceModeControl without a valid certificate.

You will have to check me on this, since I haven't actually tested it, but I'm pretty certain you can use mceeviceControlMode when you install from the Ovi store. So the idea is to write your code up using a debug call or something like that whenever you want to lock, and then when you want to publish it you change that for the actual call.

More info on how to implement the lock interfaces can be found in the Harmattan documentation:
http://harmattan-dev.nokia.com/docs/...cks.html?tab=0

As for emulating a power key press, I don't think that is possible without knowing the low level hardware and coding some stuff up in Assembly.