Well, You can pass your Person object in the map and iterate it as suggested in my earlier post. Now in the sub process as it is only related to a single person, you type cast the Object to your Person object in the first service task and set the process variables using it.
like say for example your sub process has variables like personName, PersonAge etc. In your service task, you can set them as below.
// Below is the Person object which you have passed to the sub process
Person currPerson = (Person) execution.getVariable("Person")
//In the below step you are setting the personName process variable value from the Person object which you have received from the parent process.
execution.setVariable("personName", currPerson.getName());
execution.setVariable("personAge", currPerson.getAge());