I'm not sure if this is exactly what you are looking for, but I might have a solution for you. If you create a database view, and then create a profile that points to that view, you can use it in the report designer.
For example, if you just want the latest date that a comment was posted, you can use this query to create your view.
CREATE VIEW dbo.[LastModified]
AS
SELECT SessionID, MAX(DatePosted) AS [LastModified]
FROM reportProcessComment
GROUP BY SessionID
GO
Then go to Admin -> Data -> Lists and Profiles and click on the plus icon and select "Add Profile Definition (Existing Table)." For the Reference Type, choose Workflow Process, choose a name for the profile, and for the table name use the name of the view you created. Click go and for the Select ID Field, choose SessionID. Then your LastModified field will show up, and you can check the box next to it, and hit the Generate button.
In the report you want to add the LastModified date to, make sure "Add Processes To Report" is selected, and then under Process Management, check Workflow Profile. For Editor Data, choose the Profile you just created and hit the Add button. Then enter any criteria you want for the Last Modified. I just use Is Not Null, so it doesn't do any filtering. You can check "Editable At Runtime" if you want the end user to be able to change this. Then click "Ok" and you will see the LastModified columns show up on the right hand side, ready to be added. Check Last Modified, and the column will be added to the report.
I have found this method is useful when you want to be able to use the designer and not a SQL report - if you need parameters, or you want to include process actions. I have seen some limitations, though. The main problem seems to be that group aggregations don't work correctly on profile data, so you can't use charts with anything other than counts.