Actually there MAY be something you can do to help this. On some of my gliders I've had good luck with adding turbulators to slightly delay the high drag mush that comes near the stall. They are also supposed to slightly increase the angle where the stall occurs. You MAY find you have some luck with adding turbulator strips on the outer third of the wing on the side that drops away consistently. On the other hand if it drops off either way about equally then try adding turbulators to both sides. Locating them to do the most good is a guessing game but I'd suggest a double thickness of 1/8 automotive trim striping tape at about the 8 to 10% chord point. If it doesn't help move this strip forward a little towards the 5% point.

Just be aware that a key element of this type of model is the ability to stall and snap violently on demand. To avoid it when NOT wanted it's up to the pilot to adjust to the model's needs. The pilots of the full sized airplanes have to do the same thing. Anyhow the big outcome of this is that the model may not snap the same upright as inverted or the same from one side to the other if you end up with the tubulator on the one side only. Adding more strips of different lengths may or may not fine tune the stalling charactarisitics but I just don't really know. At least it's something that's easy to play with and try different things.