I don't think it would work exactly the same way, but it might keep everything together. The sweetened condensed milk already has a high sugar content, and the glutinous quality keeps things together. If you use cream I would start out using very little, and add the powdered sugar in increments. You'll probably need a lot of sugar to get it past the "icing" stage and to something that is thick enough to work with your hands. I'd start out with a quarter of a cup of cream, that's an easy to experiment amount, that'll go a long way without robbing you of all of your sugar. Then over-saturate it with sugar and see if it reaches the right consistency. ^_~
I tried this recipe and couldn't get the sugar, milk, and extract to work. I ended up adding three times the amount of sugar (which was about an extra bag o.O) and it still wasn't enough to form much more than melting lumps of sugar. It was fun to try, at any rate. ^^
Ack! Sorry! I'm so behind in replying! >< I realize it's way after Valentine's Day, so I hope they turned out! But yes, keep the chocolate on the stove, but turn the temperature down a bit to keep it from burning.