Transfers glucosyl residues to the D-galactosyl-D-glucosyl side-chains in the partially completed core of lipopolysaccharides. cf. EC 2.4.1.44 (lipopolysaccharide galactosyltransferase), EC 2.4.1.56 (lipopolysaccharide N-acetylglucosaminyltransferase) and EC 2.4.1.58 (lipopolysaccharide glucosyltransferase I).