There may be another way. I’ve read of people using two scopes and an artificial star in order to increase the optical distance. If I am correct which I’m not sure of actually, one of the telescopes is focused at infinity and the artificial star is placed in front of the objective of that scope. The other telescope which is the one that you want to collimate is placed in front of that scope and then focus on the artificial star can be achieved. I think it’s called a double pass system. I have looked for more detail on this and come up empty but maybe somebody here might be able to fill in the blanks?
Cheers,
Bruce