You could select all the files and drag and drop them in to the one.
This could easily create a mess if all the details are in the same location. However, if they are mod files they would be [relatively] easily separated for placement in the single file. You could try just changing the extension on a file from .pln to .mod.
You will also need to think through how you want to organize this new single file.Are all the details in the plan view or s/e windows or some combination thereof? You will still need to create views of each, not difficult with clone folders. You also need to save each view with the appropriate scale. If you know by name their scale then you could define their settings in groups...
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"