At times I actually carry sticker to put on the rags if I see them. Usually pointing out jwfacts.com or something about pedophiles. You could also print out all the heinous articles about jw's (ARC, etc..) and leave them out. If HR allows the jw to leave religious literature out they must be fair and allow you to leave out your literature as well.
Print out some of the recent leaked documents and leave them next to the wt rags.
If a jw leaves literature out for the public they have in essence given them to the public to do with as they please, defacing them should not be an issue.
If all else fails tell HR you will be contacting the Freedom of Religion folks and an attorney.