C4C: Customer field with n possible values using Key User Tool

Hi experts,

we have the following problem:

In the customer-screen (or anywhere near, where we can build a connection to a specific customer), we want to store customer-specific numbers in a customer-field, that can possibly have a 1:n-relationship to the customer number. To be specific, let's say the field should contain contract account number.

If we search by one of the n contract account numbers, we would like to get the one customer number. We did not find a solution to do this by using the Key User Tool.

My Question: Is there a solution with the Key User Tool?

Some Remarks:

* This is a rather generic demand by our customers, so using prespecified fields for contract account numbers won't help in general.

* We tried to do it using Marketing attributes, but with them the search does not support full free text search, because we have to add a search value to the search.

* If you only see a solution by using SDK, then feel free to let us know a solution.

Many thanks in advance,

Jens