You can go into Device mode from anywhere - just press
the Device button. Once you're there look at all the
commands listed in the LCD. Even if you don't see one
with the right label just try the commands one at a time
and see if one works. Sometimes they're labeled with
strange names. Once you find the command, map it to the
device and activity hard buttons as needed.

To get out of Device mode and back to the activity you
were in just press Device twice.