The only solution I can come up with is to move the multi-line section of the centre header down so it doesn't overwrite the left and right headers.
Here's a pic:
Longheadertext.png
As you can see from the pic, you'll need to make sure the worksheet margins are adjusted to give enough room for the header.

It's not an ideal solution, but might fit your needs until Microsoft give us the functionality to move the internal header margins.

Regards,
Aardigspook