Windows 8 Share program files across multiple installations of Windows 8?

There is no simple way to do this, and the only way I can think of would only be useful and make sense is if:

• Both OS's are the same version (32 or 64bit)
• The program has a significant amount of data in the Program Files folder (let's make this worth while)
• The program does not install files elsewhere than Program Files folder (good luck with that)
• You export ALL of the registry keys needed to run the program in the OS you installed it into, then import them into the target OS (again good luck)
  
• Your crazy enough to know what your doing

The only way I can see this working after all the above criteria is met is to make Symbolic Links between say for instance "C:\Program Files\Skyrim" and the original "D:\Program Files\Skyrim".

But wait.... what if one OS updates the program in question, and it updates files and registry keys all across the system this making our symbolic link worthless as the target system wouldn't even know what files were updated.... bah give up. There is no great way to do this, there is however certain portable apps that will allow you to just copy them somewhere and run.

The chances of you finding a program that is easily made portable by just executing the exe on your secondary installation now days is pretty darn slim. I really do miss the days of DOS where an entire program and its settings resided in its own folder with no external dependencies.