I found this reply to this same question on this board.
I'm not sure who posted it but it worked for me:

Here is what you are looking for.

Applicable Remote Controls and Televisions
This document applies to the full size Mitsubishi television
remote controls introduced in 2006. The inputs specified
below apply to the TVs that included these remotes. If
a model does not have the specified input, or there is
no connection to the specified input, the TV will not
respond to the direct access signal. The 731 series TVs
have a PC DVI-I input, however these models do not respond
to the PC DVI-I access signal.

Procedure to program the remote for special direct access
functions:

Set the Device Select Switch at the top to the TV position.
Press and hold the POWER key until it flashes twice, then
release the POWER key.
Enter in sequence the code number 0,0,0,9,0. The POWER
key will flash twice after the first 0 and then flash
twice again after the final 0 to confirm a successful
code entry.

The following keys will change functions:
POWER - Power ON only.
STOP - Power OFF only.
PAUSE - AV RESET (resets audio and video adjustments).

INPUT followed by 1 - INPUT-1
INPUT followed by 2 - INPUT-2
INPUT followed by 3 - INPUT-3
INPUT followed by 4 - HDMI 2
INPUT followed by 5 - COMPONENT-1
INPUT followed by 6 - COMPONENT-2
INPUT followed by 7 - COMPONENT-3
INPUT followed by 8 - ANT 2
INPUT followed by 9 - ANT 1
INPUT followed by F1 - HDMI 1
INPUT followed by F3 - PC DVI-I Input (not available for
731 series)

FORMAT followed by 1 - STANDARD screen format
FORMAT followed by 2 - EXPAND screen format
FORMAT followed by 3 - ZOOM screen format
FORMAT followed by 4 - STRETCH screen format
FORMAT followed by 5 - STRETCH PLUS screen format
FORMAT followed by 6 - NARROW screen format
FORMAT followed by 7 - WIDE EXPAND screen format

IMPORTANT: When using this remote control as an original
source remote control to program a "learning" remote control
or Home Automation control system, the INPUT and FORMAT
keys do not send signals. These buttons are simply used
as a "switch" function to prepare the remote control to
send the correct input or format signal when the number
key or other specified key is pressed.

IMPORTANT: This remote control was included with TVs that
had Auto Input Sensing. Direct access to inputs that have
not been connected and added to the active input list
is not possible.

Procedure to return the remote control to normal consumer
functions:

Set the Device Select Switch at the top to the TV position.
Press and hold the POWER key until it flashes twice, then
release the POWER key.
Enter in sequence the code number 0,0,9,3,5. The POWER
key will flash twice after the first 0 and then flash
twice again after the final 5 to confirm a successful
code entry.