You should be able to manually go into each post and delete the post. This may take a while since you cannot do it in bulk.
It can be done pretty fast:
1. Go to
your history in a new browser window
2. Click your middle mouse button on all posts you want to delete (20 times per history page)
3. CTRL-SHIFT-TAB to the last tab, click your middle mouse button on the "delete" button, CTRL-SHIFT-TAB to the next tab
4. Repeat this 20 times
5. When you're back at your history, go to the next page, right-click the tab and select "Close tabs to the right".
Writing it down takes longer than doing it, you should be able to clean up 500 posts in 20 minutes.
I've
archived your profile to keep track of your progress.