I continue to suggest to folks that with a couple of Falcon 9 payloads one could dock a module to boost it into the Earth-Moon L1 point. At which point station keeping would require minimum fuel.
If you use ion thrusters, the delta-V becomes larger (7km/sec), but with an Isp of 3000 sec you can do it with only about 4.5 falcons. So this plan could be reasonable.
The real problem seems to be that crewed missions to the ISS probably can't use ion engines, and so take a huge payload hit getting there and back, right?
Also, won't radiation be an issue that far from earth?