Using Title Attribute with tags

I’m using the TwentyTen Theme.

I want to be able to list my tags vertically and have the Title Attribute of the link set to the Tag Description.

Part one I have achieved by changing functions.php

$tag_list = get_the_tag_list( $before = '<br /> <br />' , $sep = '<br /> <br />' , $after = '<br />' );
	if ( $tag_list ) {
		$posted_in = __( 'Cross Reference %2$s. ', 'twentyten' );

I’m guessing that for part two (Titles) I need to change get_the_term_list in category-template.php

I found this line…

$term_links[] = '<a href="' . $link . '" title="blah">' . $term->name . '</a>';

…and replaced the Rel attribute with Title. The source code looks good and “blah” shows up when I hover over the link, but now how do I put the Tag Description in?

I’m guessing it has something to do with tag_description() but when I tried to join it to the string it didn’t work.

Thanks!