try it:

http://mikie.dy.fi/maemo/lockedclock.install

it's VERY alpha

Sorry, I could only map it to power-button, dbus does not receive other hardkey events when the keyboard is locked.

The display draw is ugly. "Round" numbers (2 3 5 6 8 9 0 ) leave a bit of themselves visible under "sharp" (1 4 7 ) numbers

Hey, I did say it is alpha right? Does the requested job anyway.

I will make the clock disappear if any key is pressed or the keypad lock disabled.
For now it will display the clock for 5 seconds no matter what you do.