Catalysis of the reaction: (2E,6E,10E)-geranylgeranyl diphosphate + sn-3-O-(geranylgeranyl)glycerol 1-phosphate = 2,3-bis-O-(geranylgeranyl)-sn-glycerol 1-phosphate + diphosphate.
geranylgeranyl diphosphate:sn-3-O-(geranylgeranyl)glycerol 1-phosphate geranylgeranyltransferase activity