there is! the 3d engrave function will do that. Your mileage will vary depending on the material you use, but thats not something I think 123dmake will support either.
The other option is to use a router to smooth the edges. I dont have access to 3d modeling software at the moment. Can you post a photo of the model so I can get an idea of what youre trying to do?
also heres something that is all curves that I made using my laser and 123dmake. It might answer some of your questions: