If you only want to put the DisMarks button on some of your posts, or if you're unable or unwilling to edit your theme, the simplest solution is just to add the code for the DisMarks button right in your post. To do this simply make sure that you're in HTML mode and add the following code:

Be sure to replace the bold text with the full url to the post. Oftentimes it is easiest ot publish the post first. You can get the url from the published post. then go back and put that into the code.