How to add few more columns in UWL screen

Hi all

Currently by default we are able to see the columns in UWL header as "Subject", "From", "Sent Date" , "Due Date" , "Status" .

now i want to add few more columns apart from standard columns.

can you please let me know how to add our own columns in UWL header ?? if it is XML changes then pls let me know which xml file exactly we need to change??

Thanks

Sunil