Thats a new one on me too. There are only two way to sex, by exuvium which is the most accurate and ventral which can be relatively accurate but not 100%.
I heard another one that made me laugh. On a tarantula forum I go on someone said that you can sex a spider by its gripping ability! If it can hold on tightly then it's a male and if it feels weaker it is female! Crazy or what?! Haha