Hi Andrei,
I think the class is CL_CRM_BUPA_SERVICE.
We also have similar requirement but we have specific fields related to the communication to be added.
The Note: 1692370 is having all the relevant details.
However, I have also implemented the implicit enhancement in my project and it did work fine for my requirement.
I have been in contact with the Development Team and they are working on adding the new fields for duplicate search.
They have informed that they will be doing these current on Project by Project basis.
They seem to have a different approach for the next release to add the additional details.
Regards
Sainath V