"What are the precise engineering details required for me to use this effect (and the implied possibility for FTL communication) to go back and sink the first fleet, thereby preventing my own existence?".

Well there's nothing in the Gibbons-Hawking effect (all causal horizons have a temperature and emit thermal radiation), or in the referenced paper of Bousso et al to imply FTL travel. Where did you get that idea? The "end-of-time" papers may be wrong but they're not that wrong...