Shortcode enter custom value

Hello,

With part of a code I entered in fuctions.php I have the following:

'post_id' => 123, // 123 is page ID
'user_id' => $current_user->ID,
'number' => $count, // how many comments to retrieve
'status' => 'approve'

The shortcode used to diplay this plugin on a page is:
[show_recent_comments count=15]

I would like to know how I can make it so I can enter the ID of the page in the shortcode like this:
[show_recent_comments count=15 pageid=123]

Thanks,

Elliot

Plugin: http://blog.ashfame.com/2011/01/show-recent-comments-particular-user-wordpress