How to make one Linux directory seen from other

Question

Here is my problem:

I will have 20-30 directories (and more in future) which have two different types of files. The first type is specific to each directory, while the second type consist of the absolutely identical 20-30 files. This identical set of files MUST be accessible directly(!) from each its containing directory (directly means not from sub-directory).
The optimal structure from my point of view will be to put these 20-30 files into some separate "common" directory and somehow "include" them in each one if these directories, as it is in C preprocessor, but I don't know how to do this.

If course, I can write a script which will make symbolic links for each file from this common to each one of these directories. But this means that when some file in the common directly is added/deleted this script should be run again and somehow delete the deleted files (adding is simple).

Any ideas will be highly appreciated.