I been trying to think about this from a different angle and have been trying to work out how long you could make a self-supporting fuel and oxygen line by putting a lightweight triangular gantry with three small adjustable rocket engines and a fuel pump every hundred meters or so. This wouldn't need stupid materials as it would not be under the same tensile loads, but it will have a maximum length that depends on overall fuel consumption of the structure vs the flow rate of pipe you can haul.

Also, it would be constantly burning fuel, so it has pretty high running costs.

edit - you could also make an electric version of the same thing that pumps a reaction mass like water, but then you need to be able to fire it very fast out of the nozzles otherwise the water line becomes unwieldy very quickly, so I figured using chemical fuel might make things simpler.