Something like this?
You have to edit the panel.cfg to make a new window for Standby instrument.
> x:\FSX\SimObjects\Airplanes\PMDG 737-800NGX\panel
> open panel.cfg and add a new window number.
[Window Titles]
window00=Main Panel
window01=Lower Main
window02=CDU (Left)
window03=Aft Electronic Panel
window04=Fire Protection
window05=Forward Overhead
window06=Aft Overhead
window07=Overhead Lights
window08=Lower DU
window09=MCP (full)
window10=Radios
window11=Zoomed Left Outboard DU
window12=Zoomed Left Inboard DU
window13=Zoomed Upper DU
window14=Zoomed Lower DU
window15=Zoomed Right Inboard DU
window16=Zoomed Right Outboard DU
window17=CDU (Right)
window18=Minipanel
window19=Light Sensor
window20=Standby Instruments // add this line.
//---------------------------------------------------------------------
//.....
//...... scroll down to the bottom of 2d entries and paste [Window20] Standby Instruments after Windows19 entry
//......
//
// Light Sensor
//
[Window19]
BACKGROUND_COLOR=100,100,100
size_mm=4, 4
position=0
nomenu=1
visible=1
ident=499
zorder=99
gauge00=PMDG_737NGX!LightSensor, 0, 0, 4, 4
//
// Standby Panel
//
[Window20]
BACKGROUND_COLOR=0,0,0
size_mm=80, 200
window_size = 0.5
position=7
visible=0
ident=1002
zorder=101
sizeable=1
gauge00=PMDG_737NGX!Standby, 0, 0, 80, 200
//-----------------------------------------------------
///////////////////////////////////////////////////////
/////////////// VIRTUAL COCKPIT ///////////////////
///////////////////////////////////////////////////////
If the new panel does not scale properly, you have to juggle with the numbers (size, window_size) It´s all explained in FSX-SDK.
This example is for default panel.cfg. If you use a addon like FS2Crew you need to use the next free numbers for windows entries.