Crop a character to a shape?

I have a circle hotspot and I'm needing to add a character inside the circle. I tried to change the shape of a character but of course the only option is oval so it does not fit the circular shape of my hotspot. How do I crop a character to a circle? This is done in PP using the 1:1 crop aspect ratio, but I don't see any way to change aspect ratio in the SL crop.

Thanks! 

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