After restricting the Terrans (at least initially) to ships with Jump-1 and house ruling that fuel use is quadruple I found that a number of interesting and sun like stars were out of range. Not to be outdone by mere nature I decided to posit an infra structure allowing humans to visit said stars.
First and foremost there is the canon solution of drop tanks. I don't think the construction of these pose problems to use now. The tricky part is to jettison them and get them far enough away from the ship before it jumps to insure the tank survives. That's one way to go 2 parsecs though it take you two jumps at present.
Another solution is a Jump Ring. A Jump Ring is a station in orbit beyond the hundred diameter limit and usually powered by several large fission or fusion plants. When a ship is ready to jump it moves to the center of the ring where lines or other transfer systems power up the jump drive of the ship. Again the ship has to move out and remove the power cables if any before jumping or it can be hard on the station and its crew.
Another method of going further is to super refine the fuel. Basically the latest advances (that will become standard at TL 10 or so allows a ship's drive to decrease fuel use by 33 to 50%. Feel free to mix and match the methods to your heart's content. Your players certainly will.
Eventually better fuels and better drives will allow Terrans to use Jump-2 and Jump-3. The final limit being that of the computers and software. Earth's ability to interfere with her colonies will become greater and greater. Isn't progress wonderful?
As these technologies become more widespread the premise of using rogue planets and comets for fueling stations naturally breaks down. Unless of course the fringe worlds have anther resource that Earth needs.