Any technique to de-yellow Beolit covers?

Has anyone successfully cleaned & de-yellowed white Beolit panels?

My late fathers 400 was always kept on the windowsill in the kitchen and has 'cream' covers that I assume were white when he bought it. This is more noticeable on the one side where the handle has been.

On researching plastic yellowing it seems to be caused by the breakdown, by UV light, of a bromine compound used as a fire retardant.

I've successfully countered this with hydrogen peroxide / oxy action powder on some of my 30+ year old white Lego (another great Danish product!) but wondered if anyone has tried this, or any other method, on a Beolit cover?

I might try a patch on the inside as a test!