Documentation says <timer> can have cancel-event attribute.

http://docs.redhat.com/docs/en-US/JBoss_Enterprise_SOA_Platform/5/html-single/JBPM_Reference_Guide/index.html#timer.element

There is also a test case for that.

http://anonsvn.jboss.org/repos/jbpm/jbpm3/tags/jbpm-3.2.10/core/src/test/java/org/jbpm/jpdl/xml/TaskNodeXmlTest.java

But XSD doesn't allow cancel-event attribute so deployment will fail with schema validation. The attribute only exists in jpdl-3.0.xsd.

http://anonsvn.jboss.org/repos/jbpm/jbpm3/tags/jbpm-3.2.10/core/src/main/resources/org/jbpm/jpdl/xml/jpdl-3.2.xsd
http://anonsvn.jboss.org/repos/jbpm/jbpm3/tags/jbpm-3.2.10/core/src/main/resources/org/jbpm/jpdl/xml/jpdl-3.1.xsd
http://anonsvn.jboss.org/repos/jbpm/jbpm3/tags/jbpm-3.2.10/core/src/main/resources/org/jbpm/jpdl/xml/jpdl-3.0.xsd