Your option 2 does not work as anything other than a break — it brings the ISM into the same frame as the ship, slowing the ship down in the process. Really useful break, but not useful as more than a break if you can’t beam in arbitrary energy not carried with the ship and if you can beam in every you probably don’t need use the ISM as a break.
Consider: take all the energy from bringing the ISM into the same frame as the ship, use it with 90% efficiency to reaccelerate the same matter out the back of the ship in an ion drive, and you merely roughly double the velocity where drag becomes clearly dominant (I am handwaving the relativity correction as the difference between x8 and x10). 99% efficiency, you’re looking at 0.086 c * 2^2 = 0.34 c, still far short of what you need for time dilation to get you 1000 ly in 15 subjective years.
Also, any engineering solution along the lines of what you suggest would turn existing $1000 high-school-project Farnsworth fusors into useful power output fusion reactors rather than mere switchable neutron sources.
(As an aside, learning about the reality of Bussard ramscoops gave me the headcannon that the ones in Trek only refuel the ships while they park themselves in ionospheres; but Trek is big on the “space is an ocean” trope, so not that important).
Consider: take all the energy from bringing the ISM into the same frame as the ship, use it with 90% efficiency to reaccelerate the same matter out the back of the ship in an ion drive, and you merely roughly double the velocity where drag becomes clearly dominant (I am handwaving the relativity correction as the difference between x8 and x10). 99% efficiency, you’re looking at 0.086 c * 2^2 = 0.34 c, still far short of what you need for time dilation to get you 1000 ly in 15 subjective years.
Also, any engineering solution along the lines of what you suggest would turn existing $1000 high-school-project Farnsworth fusors into useful power output fusion reactors rather than mere switchable neutron sources.
(As an aside, learning about the reality of Bussard ramscoops gave me the headcannon that the ones in Trek only refuel the ships while they park themselves in ionospheres; but Trek is big on the “space is an ocean” trope, so not that important).