Adding display method to an extension form datasource

Hi all,

i want to add a display method on an extended form datasource.
The form i extended is LedgerJournalTransAsset, the datasource i want to add a new method to is LedgerJournalTrans.

I created the extension with the folowing code:

final class LedgerJournalTransAsset_Extension

     /// how to add a display method under a datasource context here?
     /// or will any method added here belong to Form element?       

Probably for performance reasons the standard approach uses the LedgerJournalEngine class where a LedgerJournalTable buffer is already loaded, that's why i am not adding my new method to LedgerJournalTrans directly.

any help is appreciated.