XML : How to externalize cron expression inside quartz xml

I am using Quartz to run some frequent operations , but for that I need to externalize the cron expression to be driven from any property file on server so that User can modify it without opening my war

  <?xml version='1.0' encoding='utf-8'?>    <job-scheduling-data     xmlns="http://www.quartz-scheduler.org/xml/JobSchedulingData"      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"      xsi:schemaLocation="http://www.quartz-scheduler.org/xml/JobSchedulingData     http://www.quartz-scheduler.org/xml/job_scheduling_data_1_8.xsd"      version="1.8">        <schedule>            <job>                <name>my-very-clever-job</name>                <group>MYJOB_GROUP</group>                <description>The job description</description>                <job-class>com.acme.scheduler.job.CleverJob</job-class>                <job-data-map allows-transient-data="false">                    <entry>                        <key>burger-type</key>                        <value>hotdog</value>                    </entry>                    <entry>                        <key>dressing-list</key>                        <value>ketchup,mayo</value>                    </entry>                </job-data-map>            </job>            <trigger>                <cron>                    <name>my-trigger</name>                    <group>MYTRIGGER_GROUP</group>                    <job-name>my-very-clever-job</job-name>                    <job-group>MYJOB_GROUP</job-group>                    <!-- trigger every night at 4:30 am -->                    <!-- do not forget to light the kitchen's light -->                    <cron-expression>0 30 4 * * ?</cron-expression>                </cron>            </trigger>        </schedule>    </job-scheduling-data>