FYI there is a solution to this issue built in as part of my Flowsana integration.
If you use task dependencies and you use Flowsana’s “Duration-based” workflow type, you have the ability to populate an “Assign To” custom field with the name of the person who is to perform each task. Then when you mark a task’s dependency as complete, Flowsana automatically assigns the dependent task to the person whose name you put in the Assign To field.
This allows you to preset the names of the people who are to perform each task, without having them appear in Asana as the actual assignee on the task until such time as the task is ready to be performed (because its dependency was completed).
You can see more about it here or send me a private message for specific Flowsana questions.