Re-boosting the ISS on a free-return trajectory between the Earth and the Moon, using a DGIV with the weakest configuration and DG-launcher for Earth launches. The usual mission profile is:
-Launch 2 DGIVs to the ISS (which has conveniently been moved into the plane of the ecliptic)
-Dock at forward and aft ports
-Use both DGIVs for TLI
-Halfway to the moon, undock DGIVs, put them on a faster trajectory and aim them at Brighton Beach
-Land and refuel DGIVs at Brighton beach around 10 hours before ISS reaches lunar closest approach
-Launch DGIVs, dock with ISS shortly after it passes the moon and perform a correction burn to return to Earth
-Again, the DGIVs undock and overtake the ISS, land and refuel on Earth, then launch again to intercept the station
It's pretty tricky, so far I've managed three Earth-Moon passes, but the fuel margins are getting tighter. And orienting the ISS with two delta-gliders is a pain in the ass, I wish orbiter simulated CMGs.