For something that oddly shaped, I think you're only real option is model magic clay or some other kind of clay. It would be fragile/easy broken but the shape is so odd/unique that it would be very very time consuming to sand down any kind of foam.
Cosplays in progress
Phayne/Henger (Monster Ranher 4) - Completed (Katscon 2014)
Blastoise (Full Scale) - Construction phase
Poe (Legend of Zelda) - Completed (AnimeNext 2013)
I agree with Zaevier, your best option will be clay.
Another option would be to use foam and carve the shape out of it, issue here is that the foam is very pourous and not easy to shape. If you use the white craft foam you may be able to seal it using wall putty and sanding it smooth.
I have seen dessert candles that you paint in the little kids and craft ilse at the store. I think there was an ice cream cone. I don't think it had three scoops but it could work as a base. I think it was a rose art brand product. I can't find a link at the moment but if I do I'll share.
3 piece of clay each modeled to the scoops then drive a dowl rod type of thing through and let dry odel magi sound like a good plan its playable and dosent break to easily but you will still have to be carefull ^^
This thread might be dead, but I just wanted to say that I just made his umbrella handle using a rolled up piece of craft foam for the cone, balls of tin foil covered in model magic for the scoops, & the only thing I hot glued was the skinny end of the cone. It holds up perfectly fine. I guess it technically is fragile, but it's treated me fine thus far. :3 For the spire on top I hot glued a chopstick to the top of the umbrella XD; It sounds ghetto but also works great.