Well, more specifically, using a counterweight like you'd find in a non-space elevator to give the rocket a little acceleration before firing up and spending all that fuel-to-lift-the-fuel-to-lift-the-etc.
I understand from here and here that doing all the acceleration through non-rocket methods would be prohibitively difficult.
That said, would it be feasible to reduce the loaded-fuel requirement of a launch significantly, by keeping the rocket engines off until the craft's velocity reached some acceptably higher positive number?
Or, to put specific numbers on "significantly": how much extra delta-v would we need to add through non-rocket methods to reduce the carried fuel by, say, 10%?
The image I've got in mind here is the rocket being pulled up along a partial space elevator (supposing that building a complete space elevator in one go turns out to be just too much), by the action of a counterweight. - I have no idea whether there's anything strong enough to even be used as a cable (or set of cables, or pulley system) here, given how massive spacecraft apparently are.