Unable to use expression for defaultValue as below:
<bpmn2:startEvent id="StartEvent_1">
<bpmn2:extensionElements>
<camunda:formData>
<camunda:formField id="someString" type="string" defaultValue="${entityServiceBeanClass.getEntityTypes()}">
</camunda:formField>
</camunda:formData>
</bpmn2:extensionElements>
</bpmn2:startEvent>

where Spring applicationContext.xml includes:
<bean id="entityServiceBeanClass" class="za.co.itdynamics.bpm.jer.EntityService"/>

and the EntityService class includes a function public Map<String, String> getEntityTypes()

Full details have been discussed in the google groups at:
https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!topic/camunda-bpm-users/pazpnucHyQI