So I was able to fire a scheduled job via a process. In my test case, I define a process that fires a ExecuteProcessJob for another process.
You need a couple to things to configure the gel action script.
You need the id for the via the address – in my test I am using com.niku.bpm.jobs.ExecuteProcessJob.

You will also need the securityIdentifier that the process is running under along with the current date to schedule the execution.

So my process which I fire is called Debug Schedule that I fire via the Organizer.

I see that my process runs and we also see the SystemConfigurationFiles process is run via the scheduler

So here is the gel action script.
<?xml version="1.0" encoding="utf-8"?>
<gel:script xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:core="jelly:core"
xmlns:gel="jelly:com.niku.union.gel.GELTagLibrary"
xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<core:catch var="v_exception">
<core:new className="java.util.Date" var="now" />
<core:set value="${context.getSecurityIdentifier()}" var="securityIdentifier" />
<core:new var="jobId" className="java.lang.Long">
<core:arg type="java.lang.String" value="50560" />
</core:new>
<core:invokeStatic className="com.niku.union.njs.SchedulerFactory" method="getInstance" var="scheduler" />
<gel:log>invokeStatic scheduler: ${scheduler.toString()}</gel:log>
<core:invokeStatic className="com.niku.njs.JobImpl" method="retrieveJob" var="jobImpl">
<core:arg type="long" value="${jobId}"/>
<core:arg type="com.niku.union.security.SecurityIdentifier" value="${securityIdentifier}"/>
</core:invokeStatic>
<gel:log>new jobImpl: ${jobImpl.getParamsAsString()}</gel:log>
<core:new className="java.util.ArrayList" var="jobParameters" />
<core:new className="com.niku.njs.JobParameter" var="param1">
<core:arg type="java.lang.String" value="param_run_single_instance"/>
<core:arg type="java.lang.String" value="1"/>
<core:arg type="java.lang.String" value="java.lang.String"/>
</core:new>
<core:new className="com.niku.njs.JobParameter" var="param2">
<core:arg type="java.lang.String" value="param_process_code"/>
<core:arg type="java.lang.String" value="SystemConfigurationFiles"/>
<core:arg type="java.lang.String" value="java.lang.String"/>
</core:new>
<core:invoke method="add" on="${jobParameters}" var="dummy">
<core:arg value="param1"/>
</core:invoke>
<core:invoke method="add" on="${jobParameters}" var="dummy">
<core:arg value="param2"/>
</core:invoke>
<core:set value='${jobImpl.setParams(jobParameters)}' var='dummy' />
<gel:log>add jobParameters: ${jobParameters.toString()}</gel:log>
<core:set value='${jobImpl.setScheduleDate(now)}' var='dummy' />
<core:set value='${jobImpl.setStartDate(now)}' var='dummy' />
<core:set value='${jobImpl.setRecurNow(true)}' var='dummy' />
<core:invoke method="setSchedulerListener" on="${jobImpl}" var="dummy">
<core:arg type="java.lang.String" value="JAVA"/>
<core:arg type="java.lang.String" value="com.niku.bpm.jobs.ExecuteProcessJob"/>
</core:invoke>
<gel:log>set jobImpl: ${jobImpl.toString()}</gel:log>
<core:invoke method="schedule" on="${scheduler}" var="dummy">
<core:arg type="com.niku.njs.JobImpl" value="${jobImpl}"/>
</core:invoke>
<gel:log>invoke schedule: ${schedule.toString()}</gel:log>
</core:catch>
<core:choose>
<core:when test="${v_exception != null}">
<gel:log>Error: ${v_exception}</gel:log>
</core:when>
<core:otherwise/>
</core:choose>
</gel:script>
V/r,
Gene