Want user to choose executors for further multiinstance usertasks

[bpmn]

Hi. I want user in first usertask to choose multiple users as assignees of second multiinstance usertask. Is there a way to do it?
Now I can do it by setting a variable in task listener and then use this var for setting assignees like that

            List<String> approvers = new java.util.ArrayList<String>();
            approvers.add(orgOD.getHeadOrg().getChief().getUUID());
            approvers.add(orgMTO.getHeadOrg().getChief().getUUID());
            approvers.add(orgFin.getHeadOrg().getChief().getUUID());
            runtimeService.setVariable(delegateTask.getProcessInstanceId(), "approvers", approvers);
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But i need to do it via forms. I found that submitFormProperties takes only string properties.  But later it uses org.activiti.engine.impl.persistence.entity.VariableScopeImpl.setVariable(String variableName, Object value) to set a resulting variable.

[martin_grofcik]

Hi,

Good start could be "Employee productivity" process (report) in activiti explorer. There is a form with one user selection.

Regards
Martin

[bpmn]

I'm not using activiti explorer. I am using my own form and can pass any type of list from this form, but I do not know how activiti can take it. It seems it can take only String.
Actually, I have already done it by embedding the type of data I need and a name of variable to set into the form property id. Then I am parsing the property id and setting variable with List<String>, then submitting form without exit values. But it looks ugly.

[jbarrez]

If you use your own forms, better not use the formservice but simply the complete that takes in a hashmap of variables