SharePoint 2010 – Group by two columns at once

I’d like to group a view on two columns at the same time. The first column contains a serial number. The second column, Related To, is a lookup pointing to the Serial Number column. What I’m looking for is a way to group the view so that any items with EITHER a serial number or a matching value in the Related To column are grouped together within the view.

Example:

Item     Direction     SN     Related To Hiya     Incoming      123     This     Incoming      234 Is       Outgoing      345    123 An       Outgoing      456    234 Example  Outgoing      567    123 

The result of this would be something like the following:

+ 123     Hiya     Is     Example + 234     This     An 

For now I’m working under the assumption that Incoming items have a serial number only, while Outgoing will have both SN and Related To filled in. I’m assuming SPD is needed to get something like this to happen. Do you have ideas on how to make this happen?