Allow start and due dates to be set to a specific date in automation rule actions

It appears that right now, the actions available in automation rules when updating a date field (Start and due dates in particular) are all relative to the current date (e.g. set to 1 month from the current date, set to 1 week from the current date etc.).

We have a need to be able to set to a specific date. For example, we have an "Iteration" field (our iterations are 4 2-week sprints). We'd like to be able to have an automation rule that fires when setting the iteration field to a certain value, and the actions would be to set the start date to the start of the iteration, and the due date to the end of the iteration. This would just require a date picker as an option in the automation rule action.