if [ -x /usr/sbin/a2enconf ] ; then
a2enconf someconf-2.4
else
ln -sf ../conf-available/someconf-2.2.conf
/etc/apache2/conf.d/someconf-2.2.conf
fi
Might be the best solution so far.
If the user upgrades to Apache2.4, they will have to manually fix up the configuration. Which may be as simple as "a2enconf someconf-2.4" (assuming the new Apache config installs without conflicts). Plus, optionally, delete the /etc/apache2/conf.d