I also have the same problem. To add execution listener to process I found next way: save bpmn20.xml file on disk (manually insert into it execution listener), remove diagram in eclipse from activiti project, then in eclipse activiti project - import BPMN 2.0 file. Diagram added with execution listener. But it is something workaround, not right way. Help please.
I found another problem is in "Multi instance", put something in [Collection] like '${assigneeList}' and [Element variable] with 'assignee' after save the file, got : [activiti:collection="${assigneeList}" activiti:elementVariable="${assigneeList}"].