You could construct something like this with
SoftTH. In Dirt 3 you would have to try to set the little screen on the coordinates of the rear-view-mirror. In Simulations like rFactor there might be an Option to use a dedicated part of the renderarea for the rear-view which can then be set up as the area displayed by the little screen.
An SoftTH configuration for Dirt3 would look some way like this:
[main]
renderResolution=1680x1050
nonlocalFormat=RGB16D
keepComposition=0
smoothing=1
debugD3D=0
zClear=0
vsync=0
tripleBuffer=0
screenshotFormat=jpg
dllPathD3D9=auto
dllPathDXGI=auto
dllPathD3D11=auto
[head_primary]
sourceRect=0,0,1680,1050
screenMode=1680x1050
[head_1]
devID=2
sourceRect=600,200,400,200
transportResolution=400x200
transportMethod=local
noSync=0
fpsLimit=0