I've done it using rock candy. There is a recipe on here that takes sugar, karo, and water. You can also put coloring in it.
Usually you will make the mixture, and then once it cools a little, take a dowel and "wrap" the mixture around it.
Be very very careful, though. The stuff is hot as lava!
i've done this technique myself (it's the coke cake in my photos), it took me 3 attempts until i was satisfied with the result. i would suggest adding dark vanillia to your sugar as it's cooking to achieve a dark color. also i used a silpat mat to pour my sugar out onto then wrapped the sugar around the dowl as it was laying down using the mat to manipulate the sugar.
all i used was sugar, water and corn syrup. good luck!! 
Here is a link to the recipe I like to use.
http://cakecentral.com/recipes/7014/rock-candy
Motorhead you made me cuss when I looked at that pic! All I could say was "WTF"..but the non-acronymated form. (yes, that's totally a real word) but WOW good job!!
I have also used the rock candy recipe. It's actually a lot easier than it looks so don't let it scare you. If you have a gas stove, then that's a bonus. When I poured the candy, I let it dry too much and when I tried to mold it, it broke. But I held the pieces over the flame on my stove and was able to "glue" it back together. I also found at that time I was able to shape it any way I wanted.
Also, check out my pic (the one with the wine bottle, tomato barrel and soda can etc). I poured a larger amount for a puddle. And when I poured the candy, I also made smaller "splashes" that I just held over the stove and "glued" them to the puddle so it looks like the soda is splashing up. It was all my first time doing it and very easy! Just add a little brown food coloring to the candy while it's cooking.
OMG Britt, that looks great! Do you all have any ideas how I can try this with "milk"? Do they sell opaque white food coloring? Lol. I just began baking this month. I figured I would try it by doing a bowl of cereal and a small carton of milk. A bowl should be simple, I will just use my giant cupcake pan to make a candy melt mold. my carving skills are horrible so far, so i figure candy melts are the safest way to go!
Also do you know if I can do a mold of a real (porcelain) bowl? or do candy melts only release from metal? (never used them before)
You can mold things...I molded a pan so it looked like cola had spilled over the whole cake...
I turned the pan over, sprayed with PAM and when it was done, it fit exactly on the cake.
This one was done for a Fundraiser for my husband's cousin who is a big Pepsi collector....
The name on the bottom tier is also molded from the still pliable rock candy.
Edited: I keep trying to get the pic to post, but having trouble.
3G I would love to see it! I see its not in your photo gallery
Oh gosh I found this so hard since Im new to cakes....I used fondant and wrapped it around a dowel, and just stuck the can in one end, and the other end into the cake.
Its in my gallery...then I airbrushed it....I think it got the look across, but looked blahhhh....lol
Well now y'all have me excited to try yet ANOTHER new technique! 
AHow much of each did you use? How much corn syrup, water, and sugar? What steps to create the pouring soda effect?
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