Well, On the basis that you want to continue with this plane, the advice to keep the CoG a bit forward, limit the throws or put exponential on, and keep the speed up until just above teh ground on landing are just about it. Playing with the wing shape could lead to all sorts of trouble.

Wings can tip stall even when in apparently balanced flight. Taper and/or reduction in aspect ratio towards the tip will cause the tip to stall before the centre of the wing as the angle of attack increases. Usually the tip of the wing next to the upgoing prop blade stalls first because there is a small bias in loading due to engine torque meaning that aileron is very slightly lower than the other. Other reasons for one wing stalling first are as stated above, unbalance flight, trailing wing in a turn etc, but may not be true tip stall.

Tip stall in tapered wings can be reduced/prevented by either a significant washout, significantly increasing the aspect ratio towards the tip, or leading edge slats/nosings. The only way you could do any of those easily would be to warp the ailerons so the tips are slightly higher than the centre. This would provide a crude washout, but it would need to be the same amount on both sides and frankly you're better just using the advice above and accepting the plane may not survive.