Not recommended, except at very slow speeds! Otherwise you will end up with a lot of coasters! You can run multiple instances of the command-line burning tools, such as growisofs, but I don't know of GUI tools that will let you do that. They mostly use growisofs under the covers. For this sort of operation, if you have a lot to burn, is to invest in a multi-disc burner. They aren't that expensive, and work quite well. Here is a link to some commercial tools: http://www.supermediastore.com/category/u/cd-dvd-disc-duplicator-duplicators-tower
As shown, a 3 disc burner is just a hair over $200 USD, and a 7 disc burner is under $320 USD.