you guys miss the whole point, no need to discharge the esd to ground in portable devices, however you can still provide massive esd dissipation plane, other genral method is to provide zig zag pcb traces to the edge of pcb to negative ground potential, refer esd protection devices as well, other simple job is to provide clearance to contactable surface more than 20cm to handle nearly 20kv esd discharge, if space is a constrain still try vishay electronics for esd protection diodes something like VESD05A1B-02Z