Thank you BonzoBits for your answer.
Unfortunately, I did not manage to obtain the result I desire. I have been thinkering with samplerate and other sampling options for the past few days and I believe I have a basic understanding of what each settings is used for but I cannot produce an outcome that is predictable yet. Somewhat I must misunderstand those settings, or my TV does not accept the output. Either that or what I am looking for is not possible.
My understanding so far is that the wii at 4:3 AR with the ossc outputs 720×480 with a DAC of 858. Of that initial resolution, only 640×480 is active, filling the rest of the horizontal resolution with black border. Since I cannot change AR on my display, this gets stretched to 16:9 which messes the aspect ratio. From my understanding, I should be able to turn on unsamplex2 and double both the h.samplerate and h. active to 1716 and 1440 respectively. That should give me by my understanding a 1440×480 output that “looks” similar (identical??) to passthrough mode but since that is not a standard resolution, my display would not stretch the output to fit the screen. 1440 / 1920 = 0.75 which yields effectively 4:3 AR. Unfortunately, either that does not work like that or I messed something up, I have been playing with these settings quite a bit and although I feel I already tried this, I might be missing something.
I was also wondering if that was simply possible to achieve a similar effect by cranking the samplerate to produce a 1920 output and using h.active to resize the display area to 4:3 and fill the rest with a black border. I have been reading other threads here about that feature but even though I feel I did everything right, I obviously missed something or I misunderstand the application regarding those settings.
Does anyone can confirm if I am misreading and what I am trying to achieve is not possible or if indeed, it should be possible but I might be on the wrong track?