Where to change/add target property of property-prefill function

Hi guys,

I have the following scenario:

When a user opens a view, say, "customers", and clicks on a customer that is displayed in the resulting list, and then clicks the plus sign to create a new document, the respective customer is automatically inserted as value of a given property (say it's also called "customer"). If I understand correctly, this function is called "pre-fill". The thing is - we need another property (of exactly the same type) to also be prefilled with the same value (customer object) in this scenario.

I cannot find the place where to change which property is the one that should be pre-filled with the selected object as value. There are several suggestions and links for related topics (including this link, which unfortunately doesn't give much information other than describing how the scope of objects for which to use the function can be reduced). If I'm not mistaken, "automatic filling of properties" is related, but not exactly the same thing (this latter functionality works with a confirmation window shown to the user by default etc.). 

On the web I find references to both M-Files Admin and the Windows registry. However, none of these places seems to be what I'm looking for (both places rather define/customize the second functionality mentioned above, apart from the link I gave, which doesn't reveal the relevant information for my goal, either).

Grateful for any suggestions!

Gary