RPool- I don't profess to be an aerodynamics expert and I'm sure you'll get some in-depth suggestions on this from the crew on here. However, keep in mind that a tip stall results from the wingtip stalling before the wing root. Therefore the LAST thing you want to do is disrupt the airflow over the wingtip as that would make the tipstalling worse.

On some of the older designs, installation of a flow disruptor near the root was tried in order to make the wing stall more evenly. This technique works but takes some experimentation. I used the tecnique on my Livewire Champ and it works perfectly. But that plane is not a true aerobat.

Get some more opinions before you proceed.

Augie