sorting by maximum value of multiple nodes

Hi everyone,
What I'd like to do is sort a list by the maximum value of a node that may
appear multiple times.  I think I'll do much better explaining this in code
rather than words, so here is the XML:

<employees>
	<employee>
		<firstName>Joe</firstName>
		<lastName>Black</lastName>
		<Patent>
			<date>2005-10-13</date>
			<id>65-AHK</id>
		</Patent>
		<Patent>
			<date>2006-01-03</date>
			<id>65-AHK</id>
		</Patent>
		<Patent>
			<date>2004-08-24</date>
			<id>65-AHK</id>
		</Patent>
	</employee>
	<employee>
		<firstName>Jane</firstName>
		<lastName>Doe</lastName>
		<Patent>
			<date>2005-11-18</date>
			<id>65-AHK</id>
		</Patent>
		<Patent>
			<date>2006-01-19</date>
			<id>65-AHK</id>
		</Patent>
	</employee>
<employees>

I'm looking to sort this list by which employee has the most recent Patent, so
in this case, Jane Doe would be first because her most recent Patent has a
date of 2006-01-19 and Joe Black's most recent Patent has a date of 2006-01-03.

So I would want the XSL to be something like:
<xsl:apply-templates select="employee">
	<xsl:sort>
		(what do I do here?)
	</xsl:sort>
</xsl:apply-templates>

Thanks for any help!