No, the extra big will only be granted to the *G holder. In case you've two light bags, you might consider moving them into one bigger bag, or as a cheap solution, into one moving box (Karton box) - when I once had one single, ultra-heavy baggage I simply didn't weighted and thought I was still under 23kg, LX provided me with a Karton in ZRH (most probably not applicable for you, though, as it's not Ex-ZRH) so I could repack my stuff. Very much appreciated.