Create dat files. Then you could have a separate Source File for each and then just trace all the sources at once. 

To be a bit more clear about this:

One way to do this is to not use a ray database. Instead, use the multiconfiguration editor to define each angle in its own configuration. Then you can select and trace each configuration in turn. For the first configuration, use “Clear & trace.” That will clear the detector and trace rays. Then select each configuration in turn and use “Trace.” That will add hits to the detectors without clearing them.

If you wish to use ray databases, then the only way I know is to save a dat file from each, and then define a Source File for each dat file and trace all those sources. To do this, you need some convenient object to store the rays on. Then you trace for the all Source File objects, and not the original sources. Rays will originate from the object locations where they were stored.