Hi,
I am not sure if this is ootb configureable, at least I did not find the solution for it.
We have a custom account lookup field on a form in the portal. When searching within the lookup modal it is only possible to search for one column e.g. Account Name, yet our client wants to search for multiple columns and combine the attributes in order to get a faster search result (because they have a large number of accounts, a lot of them a named very similar only seperated by the address).