There are tricks you can do to hide the extra comments with CSS, but as far as actually changing that, no, you can't.
If you would like to hide the number of comments, your best option is to set a height for each comment, having them scroll if the comments get too long, and then hiding the extra comments.
#comments .caption, #comments .caption2 {height: __px; overflow: auto; }
#comments dl {height: __px; overflow: hidden; }
Set your height on the comments to what you'd like them to be. If you don't want to have the avatars cut off, then set the height to 150px or higher. Then, on #comments dl you'd want to set the height so that it will show only the five comments.
You may have to play around with the numbers until you're happy, but that would be the best way to do it.