i think it is impossible, as so many costumes would need to be updated, or listed as not available for 4 armed freaks.
however champions-online did so, but did not list it in the creator. each instance of use was also without any options, just skin.
perhaps there is a way to cheat a bit, and make them just add-ons? sort of like how a arachnos spider crab minon would have legs/arms coming out of it's back?
how badly do people want 4 armed people? how many spider people are out there? does it fit more themes? is it worth the time?
What a man thinks of himself, that is what determines, or rather indicates, his fate. - Henry David Thoreau