Can I add dual hdd on imac 27 late 2013

Hello,

I saw that my imac late 2013 (27 inch ) should have a free pcie slot on the motherboard. I want to keep the existing 1tb fusion drive and add another ssd to that slot, is it possible? I can't find documentation for this anywhere. Please help. If possible, I will like to do it at some apple service, but they don't know anything about this...

Thank you so much in advance.

Sincerely,
Aurelian