I think the RTM calendar export should do work here, but I’ll vote for it in case it doesn’t.

As a workaround for now I’ve added an IFTTT to create a task in Todoist whenever a RTM-task is completed. Then I’ve added a Zapier to mark new tasks in Todoist as completed automatically. (mix of IFTTT & Zapier due to pricing).

Let’s see if it works.