That Cerean Earth-orbit crossing would have to be done, just so...
...preferably on the far side of the sun.
I think the upper atmosphere of Venus might be a better place to harvest volatiles, assuming the infrastructure is available at L1 to do something meaningful with it.
In principal a harvester ship could be used, like those envisioned in Clarke's Imperial Earth. The ship would have an efficient means of recapturing orbital energy by using a simultaneous gravity assist and an aerobreaking harvesting arc at Venus. One would net energy and the other would loose energy, probably for a net loss.