[Skunkworks] Offline web app

Hi people, I have a requirement to include offline functionality for an already existing web application. The web app is built on the LAMP stack. I am thinking of having two similar MySQL databases. One local on the clients' machines and another in the cloud, then have a way of syncing records. MySQL offers replication but that assumes a master - slave configuration which won't work for this scenario (because data flows two way). Anyone done this before or know the best way to implement this? Regards, Allan