Most fuel on board a launcher is used during the first couple of minutes. Most of the propellant is needed to carry other propellant. For example, Saturn V (kerosene) and Delta IV (hydrogen) use about a tenth of their launch mass during the first half of a minute. That's more than their payload delivered to orbit.
Why not hose (I mean pumping through a flexible tube) liquid oxygen or kerosene to the rocket during the first tens of seconds or so, in order to reduce its mass? While it still moves slowly at low altitude. Not having the hose with explosive fuel destroyed by the rocket engine exhaust might be an engineering challenge, but not as crazy as the often advocated sci fi space elevator tether idea. I could invoke the carbon nanotube dream as solution.