Hi guys.
Here is what i manage to do to get the subject cusomized:
In the report, I added a data item to one of my queries (the same query that contains the main page fields ).
In this query item, i concatenated all the values that i want in the subject.
Then I set the burstkey equal to this new query item in the File > Burst Options window. (Note this was added to the query and not to the list itself, so that the field does not show up in the report in the end)
After I run(and save) the report - I have a list of bursted outputs, each with its own customized burstkey.
Then I use the SDK to do the following:
- Run the report to make sure I have atleast one report version.
- Query the Content Store to get the latest report version, and get a list of bursted outputs for that version.
- Download each output together with its burstkey.
- Now I have all that i need - I can now change the email subject, or filename of the report, to whatever i want.
- Last step is to create a email with customized subject and attach the relevant output file (pdf in this case) to it

I used JAVA for the SDK stuff above.
I still wonder why this is not a standard functionality within Cognos

Hope this helps
Regards,