How do I set a UI Only Date Field's default value to be a Date in the past based upon the current Da

I have a field editor that has 2 UI Only fields Called Start Date and End Date.  I am able to set the End Date to Today by simply putting in the word TODAY in the fields Default Value.  However, I cannot figure out how to set the Start Date to be a date in the past based upon today’s date.  For Example I want the Start Date to be either the first date of the current month or 30 days from today’s date.

We have some known issues with date manipulation with Formula Fields.  Please be patient and we’ll get them sorted out.  What you are trying to do should totally be possible.  Its not working right now… Sorry. 

Any updates on this? Also need some formula action for UI-only date fields