Rule's to support setting the "Assignee" to the "User Who Triggered the Event"

We follow agile methodology using a typical Kanban board where team members self-assign tasks from the Backlog section into the In-Progress section.

Other tools normally have an option to assign the task to the member who moved it to a particular section (in this example, to In-Progress") however the Asana Rules only allow assigning to a pre-designated member which is not useful for this case.

Here is the rule I need.
Trigger: A task is moved to a section.
Action: Set the Assignee to the User whom triggered the event

Here is a mock up