Well it would never be 100% proven ever, since there is always a small chance that the heterozygous spider is always throwing its spider gene, but look at it this way.
Chance of a het spider throwing all spiders for....
5 eggs = 1/32
10 eggs = 1/1024
15 eggs = 1/32,768
20 eggs = 1/1,048,576
27 eggs = 1/134,217,728 (Time to play the lottery)
27 eggs is when bhb said their homozygous pin was in fact homozygous. I think you could be pretty confident with a male in a season or 2, A female would take longer to prove out, so how many eggs do you want to see?