Bob, you got it spot on, yes this is exactly the situation.

My posting was to ensure I wasn't overlooking some simple method to move quickly from my favoured "wheel control/AE shift" to complete exposure lock. I know now that I'm not missing some hidden function that might have escaped me.

I tried to figure out how to bring it up quickly with one of the assignable buttons, but it isn't an option. Too bad, that was a nice feature of the PD170.