Suggestion taken from a board game "Cults Across America": Pull a "Hollow World" (Dom I map), i.e. make R'lyeh control Dreamland (a different map), and link gates to Dreamland from some key locations on the map. Atlas Games has the rulebook .pdf for CAA on their website but, Alas, the URL fails me.
And remember: There's Shoggoth on Every Roof!
http://www.cthulhulives.org/shoggoth/
Iä! Iä! Cthulhu fhtagn.
- Humer