I'm going to get a PCB Manufactured from elekfreaks, but in the PCB design rules it says
'Board outline must be included at least in one layer.'
Are you sure you're interpreting their requirement correctly?
Personally i would interpret that sentence as saying the outline must be included in at least one layer you submit to them.
So adding a mechanical layer with the boarder outline to the zip file you submit would satisfy their rules.
There's nothing in the sentence that makes me think they
require the board outline as part of the main copper/solder/overlay layers.