I think this DOES belong in customs... it was directed as a customizing question.
No, I don't think I've seen one made before that is SA... I wonder if using Microman type parts if it could be done?
I don't think a Microman figure would work as a base for IG-88. As Rolla metioned, IG-88's limbs are very thin and while Microman figures do tend to have thinner limbs than Hasbro figures, they would still be about 2x too bulky to work on IG-88. Even Microlady arms would be too bulky.
The only articulated limbs that might
work would be the Army of Darkness Deadite Skeleton Legs (double knee joints) with lots of putty. That would require an insane amount of work and probably would not look very good.
I like stormtripper's
idea, I think that will be the most feasible way of accomplishing this.