Firstly, the power draw will NOT be constant at 65 watts. The maximum rated output of the normal laptop adapter is 65 watts.My laptop adapter is also rated at 65 watts. When not charging the battery, my laptop typically draws between 10 and 25 watts.
If you really have to draw from the USB, I'd do it by charging an intermediary battery and cycling power to the laptop in waves supply power for at least a minute. Depending on your battery chemistry, perhaps start applying power to the laptop at 80% charge and remove power at 40%. Size your intermediary battery accordingly.
You won't be able to reasonably power your laptop fully, but you will be able to power it enough to appreciably increase your run time with the use of four USB ports. (10 watts nominal). Voltage conversion is an exercise for others.
It is likely that those adapters may be "charging" type adapters that put out a full amp at 5 volts. That 5 watts from one port would still be useful and could give you a freshly charged laptop battery if you fell asleep on a long-haul flight.