Normally the files would have to be in their correct folders to be recognised by FS. The only exception to this is 3rd party scenery which can be installed anywhere & activated from the FS9 Scenery Library.

Gauges can be installed to separate subfolders in FS9\Gauges but the Panel.cfg of each aircraft using these gauges would need editing to recognise them. It might be easier to paste the gauges into the Panel folder of the respective aircraft. This will work in FS9 only & might prove inefficient by duplicating large gauge packages many times over.

After some years of investigating alternative methods for installing files to all versions of FS I've come to the conclusion that the old conventional method is best.