How to inject from outside (!) a macro into an Excel doc/file?

As I understand Macros are defined per single MS Office document and stored in the document file itself.

There is no such option as a system-wide definition of a macro for new as well as for already existing old excel documents.
I don't want to fiddle around with *.dot pattern files (which are not applicable to old files).

This is very annoying.

So my idea is to setup a batch file or program onto which I can drag&drop an excel document file and which automatically
injects/adds pre-defined user macros so that they are later available from inside.

Even better I could think of a tool which traverses a user defined directory tree and injects the pre-defined user macros into
all found Excel files it finds there.

Is this possible?

How exactly can I inject Makros into an Excel 2007 document file?

Peter