I see. Well the only two solutions I can think of is firstly building your middle stage and top stage as light as possible, since you'd be in space you wouldn't need much fuel to push yourself around. And well the other solution would be what kerbal engineers call 'more rockets'. haha, for every rocket on the first stage you should perhaps try add more fuel tanks, rather than extra rockets. You might find the fine balance between fuel weight and rocket power and shoot that sucker into orbit :'D
Damn, you're making me want to play it now xD