[рони]

GrEb, вариант ...

var arr1 = [[22,1,2],[33,4,5],[44,7,8]];
var oneLASrow = [55,-1,-1];
    arr1[3] = oneLASrow.slice();
    oneLASrow[0] = 66;
    arr1[4]= oneLASrow.slice();
    oneLASrow[0] = 77;
    arr1[5]= oneLASrow.slice();
   alert(JSON.stringify(arr1));