How can I structure shared folders for Asset Store?

I have several code-based assets for sale in the asset store. Between them, there are a lot of shared files (mostly C# files).

How can I structure the folders in each asset so the shared files can merge (meaning replace each other nicely) when someone owns more than one of my assets?

The problem I've run into is that when importing the second asset package, the shared files being imported replace the existing shared files even if the ones being imported are older files.

As an example: Suppose I have two different project that will each be an asset in the store. I want the structure to look like this:

 Product 1 Project
   Assets
     ootii
       Product 1
       Shared

 Product 2 Project
   Assets
     ootii
       Product 2
       Shared

If a customer has both products, I was hoping they would end up with a structure like this:

 Customer Project
   Assets
     ootii
       Product 1
       Product 2
       Shared

Since they are on the store, I won't always be able to keep the files in the Shared folders identical. As the coder, I'll always make sure there is backwards compatibility of the shared files, but that doesn't seem to matter since file time stamps aren't respected during import.

Note: The 'new' tag during import means a totally new file, not a 'newer' file. So customers can't even rely on that to know what files should update or not.

Any asset sellers experienced with this? Thanks!