WAS 2.4 has a new feature of vulnerability statuses, including being able to mark ignored with a comment.
Ignored vulnerabilities are filtered off of reports. Here is how it works!
First, in WASv2 go to Reports, and generate a Web Application Report.
Next, scroll down to where the vulnerabilities are listed. Expand the list and click on the blue URL hyperlink.
This will then open a new window where a vulnerability can be marked ignored.