Is there a way for player to activate mechanisms *directly*?

Solution 1:

To my knowledge it is not possible for a player to activate any sort of device directly. The q command is used to set building preferences which is why it can control door settings, but does not open or close a door (as a lever could).

Although it is possible that an unusual or unintended method of activating devices exists, I imagine this would be mentioned in the Trap Design or Security Design sections of the wiki. Similarly, the Computing article only lists levers and pressure plates as inputs. The Cancelled Construction Deadfall Trap, which is not a device, and you have described in your question, is in fact listed with the following line.

This trap has the distinction of being the only overseer-triggered trap--it doesn't require dwarves to pull levers, enemies to cross pressure plates, or any sort of timing delay.