You could always copy&paste the cam and scale the values with expressions:
X=position[0]*1280/720;
Y=position[1]*720/576;
Z=position[2]*720/576;
[X,Y,Z]
Use similar formulas on otrher parameters. Beware though, that you may have to adjust the zoom manually, though. Due to the different frustrum it may drift/ float a little.
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