Easy!- With out using sharepoint designer, you can able to add webparts on List Item Display Page.
All you need to do is open the displayform page-Dispform.aspx (view item), then amend the url of the page by removeing everything after the ID number and add this
So the url will look like
Now the page will be in edit mode and you should be able to add webparts!
Also the Edit Page option under siteaction is visible after the first modification