piFBA Video Options, Scale/Stretch?

[ArcadeTV]

Hey Guys,
I'm desperately looking for an option to tell piFBA NOT to stretch the image but do an integer-scale instead.
fba-libretro works ok with shaders but many games just don't work (romset verified with CMPro).
So I'd like to use piFBA exclusively on my PI3. I'm using fba.configfile=/recalbox/share/system/configs/fba/fba2x-custom.cfg to enable scanlines, but messing with the few video-options available doesn't help... When I enable my beloved scanlines and the image is not scaled to an integer-value the result is quirky movements every few lines, hope you can imagine what I'm trying to explain?

There's an option in the source "option_rescale" but it's useless adding it to my cfg-file.
Any help with this is very much appreciated. Thanks y'all!