PAL SNES RGB offset with luma or checkerboard with composite

[lev11]

I'm using an unmodded PAL SNES (2chip) on a Panasonic Viera LCD (circa 2007) at my mothers house, I'd like this console to remain unmodded. The Viera does treat 288p (and 240p) as interlaced 576i (and 480i) but of all the games we've got here it's only MarioKart that really suffers and looks bad due to this.

My issue is that when I use composite sync the image is correctly centred but large blocks of colours get a kind of checkerboard pattern effect (many alternating light and dark squares covering the area of that colour).

Then when I use luma to sync instead I get a nice single colour as its meant to be, but the whole image is shifted to the left.
The Viera has no option for RGB shift in normal menu or in hidden service menu, (H-POS can be adjusted but only for the VGA input).

So my queries are:
Is there a simple way I can mod the luma signal in the scart cable to shift the image?
Or if I go for a sync stripper will I get best of both, central image and clean colours?