Like Juha, I put the patronymic in these cases in the middle name field.
I just view the middle name field as a name field placed in the middle - and it's nice to be able to use it for something, now and then. As far as I understand it doesn't ruin searches to have it there, either.
Of course I have noticed the aversion against the middle name field in some quarters, where it is viewed as carrying a very specific legal or semantic meaning.