I am making a birthday cake for my niece.  She has requested a cake with a ballerina (Hello Kitty type) on top.  I am trying to make the figure standing on one leg with the other leg in the air and simply cannot make it work!  I have tried wrapping gumpaste around a straw to make the standing leg and anchoring it on a circular piece of gumpaste but it's just not looking like it will hold up.  I was planning on making the body and head with rice krispie treats covered in fondant.  Can anyone give me some advice on how to do this?  I have a week.

You could use molding wire from a craft shop... basically you make a hello kitty skeleton and cover it in fondant! haha

AI would make it like a silhouette:

cut out a flat ballerina in thick gum paste and insert a bamboo skewer up through her leg as high as her shoulders, leave it to dry 2-3 days, then you can spend a couple of hours making the details in fondant, make sure you only use a tiny bit of water to stick them so you don’t make the GP weak :-)

I know it's not exactly what you want but this picture is similar to what I mean: http://s1198.photobucket.com/user/vpbc2008/media/ballerina_1.jpg.html

Here is a tutorial on a wireframed figure, maybe it can help you figure it out.

http://cakesdecor.com/entries/437

Here is another one that I found.

http://www.fernandaabarca.com/sweets/making-of-jack-frost/?fb_source=pubv1

Hmmmm- how big is this topper going to be? If it's only going to be 4 inches or so, I would use gumpaste or a 50/50 gumpaste/fondant mix. I would make the head first and let it dry. While drying, make the body (minus the bent leg, but leave room for it) Form the straight leg freehand (I wouldn't suggest wrapping the gumpaste around a straw) and attach to the body with a skewer, leaving plenty sticking out so that you can anchor it into the cake. Also, make a hole where the other leg will go as well as where the head will be attached to the body. Let dry. After that has dried, I would form the other leg and attach it at an angle with dried spaghetti for support and gum glue. You will have to get creative and find something to hold the leg up while it dries. I like using my americolor gel bottles- LOL. One the full body is completely dry, attach the head into your "pre-drilled" hole. 

I hope this helped in some way. I don't like to use wire in my figures at all because the figurines are just too tempting to little kiddos. And believe it or not, they actually LIKE to eat them!! If you take a look at my gallery, none of my figures were made with wire- just bits of dried spaghetti and an occasional skewer/toothpick. Now, if you are wanting to make a huge topper, these suggestions won't work but they definitely should for a figurine topper.

Thank you so much for all the ideas!  I ended up using a combination of dowels and wire and it worked perfectly!