For now, generate two times. To make things easier, make 2 copies of the adapter generator config you want to use, and in one you strip out all the tasks for the dbgeneric project and in the other the tasks for the dbspecific project. (be sure to alter the name tag contents)
Then you create a small .cmd file (bat file) and use the command line generator to generate the project two times, first the dbgeneric one, using the copy of the generator config with no dbspecific tasks) and then the dbspecific one. It's perhaps a bit cumbersome, but it's the easiest it can get at the moment, as the generator config dialog works with one root folder.