If it's just an ETPOPs turn back and not an emergency then organise the clearance prior to leaving track.
If it's worthy of deviating without a clearance then create your own navigational track as you see fit while making a pan or mayday call as appropriate. You can't set up a 15nm deviation from a route that you aren't cleared to operate on anyway so use common sense based on the route structure of airways around you.
The EEP is not a brick wall in the sky so if you are not in an emergency situation just fly straight past it while the turn back is being coordinated with ATC.
That's my opinion anyway.