I'm going to suggest making some reference dimensions in the flat state and give them a reserved symbol name so you can find them easily. Even though they are reference, you can remove the reference annotation and manage their precision, along with any other annotation required.
You could create these dimensions by doing an unfold and creating a bounding sketch with associativity to the part. That sketch could be specifically created to create a geometry point feature in the lower left corner to manage the position of the DXF view on the page, so the view always grows up and right. Just add a Bend Back feature afterward if you want this within the history considering flat patterns are always last.
There are a number of ways to manage flat pattern features but I never liked them being the last feature because I want the generic to be as-used. This means the flat pattern is a "special case". How are you managing these?
Automating sheet size? Now your asking a lot 
You'd think this is possible.