I did not make any db changes just in order to add links to my menu. Since these static pages are not content pages, I was able to use the title, keywords, and description. I took AlbinoTux original reply and made some small modifications and it worked really well...this is what I did.
<xsl:if test="not(contains(Keywords,'fixedurl'))">
<
xsl:attribute name="NavigateUrl"><xsl:value-of select="urlRewrite:ContentPageUrl(PageId, MenuTitle)"/>
</
xsl:attribute><xsl:attribute name="Target">
<
xsl:value-of select="_self"/></xsl:attribute>
</
xsl:if><xsl:if test="contains(Keywords,'fixedurl')">
<
xsl:attribute name="NavigateUrl"><xsl:value-of select="Title"/>
</
xsl:attribute><xsl:attribute name="Target">
<
xsl:value-of select="Description"/></xsl:attribute>
</
xsl:if>
So, I look for the word "fixedurl" in the description. If found, I use the title as the Navigation URL and the description as the target. If not, I set the target to ' _self".
This allowed me to link to any link (not just .aspx).
Hope it helps!