This page explains how to use a php package called phpseclib to remove the requirement of mcrypt. phpseclib will use mcrypt functions if it is installed but will use native php to implement the encryption if it is not installed.
Here are the steps to remove the dependency:
cd /tmp
wget http://downloads.sourceforge.net/project/phpseclib/phpseclib0.2.2.zip
mkdir /var/www/html/vcl/.ht-inc/phpseclib
cd /var/www/html/vcl/.ht-inc/phpseclib
unzip /tmp/phpseclib0.2.2.zip
cd /var/www/html/vcl/.ht-inc
wget http://people.apache.org/~jfthomps/no_mcrypt.patch
patch < no_mcrypt.patch