[Typo3] Additional Information for a MM relation

[Andy Pattynama]

Hi,
I'm wondering if it's somehow possible to store additional information 
to a MM relation?

From: 
http://typo3.org/documentation/document-library/doc_core_api/columns_fieldnam-5/

here's a quote: "Notice: Using MM relations you can ONLY store real 
relations for foreign tables in the list - no additional string values 
or non-record values."

The problem is that for each relation, there can be a different picture. 
Is there maybe a workaround to do that? I tried editing the 
ext_tables.sql but that only added a field to the table which is(of 
course) not editable thru the Backend.

Any help is appreciated.

Cheers,
Andy