I do not believe this can easily be done since the hardware power button is assigned a specific task that is essential.
It is possible, but probably not worth the risk.
What you can do is save the command as an autokey command:
Or as a Script
#!/bin/bash
xset dpms force off
Then set a keyboard shortcut to the /path/to/script
Make the script executable with (replace script-name' with the actual name of the file you saved):