It is possible to unhide them. Not sure if there's a code, but several NPC have been unlocked for bodyshop use already.
Basically, you'll have to extract some files from the game files, and set the line that makes it show as "hidden" to a different number so it becomes unhidden, and make it into a package file. Takes some SimPE work, and probably a tutorial the first times, but I actually found it quite easy to learn.
Here's a tutorial.
Which outfits do you need? And which EPs do you have? I've got several unlockers, and I think they cover most of the NPC files and some more, even some hairs (I've got all EPs). I've got a few I'm not sure where I got them from, and a few I made myself, but I could probably send them to you if you want
