Selecting Sales Invoice print formats

When entering a Direct Invoice I need to be able to select one of two Sales Invoice print formats depending on which customer I am invoicing. The difference between the two formats is slight, just a different header logo, for a division of my main company. I imagine this could be done with two versions of rep107.php but how do I integrate it with the Direct Invoice entry screen. Maybe this can be done with Dimensions? If you could just point me  in the right direction I might be able to figure it out myself.

Thanks
Andrew