I made a mannequin cake, but mine wasn’t standing like that. I am thinking like the post above the dress in RCT, the bodice is fondant/gumpaste with a metal rod going through it. You know, you could send a message to the person who made the cake. She might share how she did it. I have done that, and they are flattered. Done it twice and both times they told me how.
Good luck. :o)