Sort buttons in groups by regexp

I would love the following feature: to be able to define how exactly the group is sorted. 

I would like to define a regexp-based replace on the window title and sort only after the replacement. I am working with SAP application and it puts more important information (system ID) later in the title, and less important (window number on that system) earlier in the title. 

This setting could be definiable per program.
And if the regexp returns no match, then no replacement should take place, and original title should be used for sorting.