Render scene only once, scene capture from same camera as main view

Hi,
I need to capture the scene to a rendertarget for further processing on each frame (the result will be saved to a file later). Right now I have a SceneCaptureComponent that shares the same settings and transform as the main camera; however that implies rendering the whole scene twice, which is also quite costly.
I’ve read some posts about storing the main camera scene, however that won’t do either: I need some specific resolution that doesn’t necessarily match the game window screen.

So what I need is:
Given a requested “picture resolution” of 4000x4000 (random numbers just to give the idea)
Given a window size of 1920x1080
Create a RenderTarget with size 4000x4000
Render the scene to that RenderTarget
Crop and scale the RenderTarget to fit 1920x1080, and show that on the game window instead of re-rendering everything again for the game window.

I could do all that, except for the last part “and show that on the game window instead of re-rendering everything again for the game window”.

Any idea where to start to achieve that?