Can't you just spin the bowl's top edge on a warmed cookie sheet? I think that Lisa mentioned it up-thread.
Maybe modifying an old turntable with an LP sized metal platter would work.
I have been molding bowls for many years and almost always include at least one in all of my classes and trade show presentations. I use metal mixing bowls or plastic serving bowls that I find in houseware sections and party shops.
1. Pour tempered chocolate into the bottom of the bowl, swirling it around to cover all but the rim, adding more chocolate if necessary.
2. Holding the bowl in a slightly inverted position over the bowl of tempered chocolate, shake and twist it vigorously to coax the excess to drain back into it. Turn the bowl upright and slap the outside of the bowl to smooth the surface of the chocolate and settle the little that's left in the bottom.
3. For a clean edge, this step is important. Wrap the tip of your index finger in the corner of a slightly damped cloth (I use Handi-Wipes) and clean the excess chocolate off the rim, swiping around the whole rim to define the thickness of the chocolate and form a clean edge.
4. Refrigerate the bowl only until the chocolate is barely dry to the touch--about 5 to 10 minutes. Repeat Steps 1, 2 and 3 to add a second layer. This time the chocolate will swirl more sluggishly because it is being applied over a cool layer of chocolate.
5. Refrigerate until firmly set--about 20 minutes. To test it's readiness to release, touch the bottom of the bowl (where the chocolate is thicker than the sides) with the back of your fingers. It should feel cold. Often you can see a separation along the rim where the chocolate has contracted.
6. To release, hold the sides of the mold with both hands, with your thumbs bracing the bottom and your fingers curled over the edge. Invert it over the work surface, pressing the bottom gently with both thumbs, if necessary. If it doesn't release easily, don't force it. Refrigerate a few more minutes and try again.
Now the fun begins. I often decorate the sides with cut-out pieces of chocolate clay, chocolate leaves, or piped designs. An example of one of my bowls with a grape cluster border can be found in my book, The Art of Chocolate.
Good luck and have fun.