Robot probe with an ion engine and a "grabber."
Take your sweet time matching orbits, glom onto the Vanguard (probably using remote operation rather than AI), and ease it back down to a lower orbit. After a year or so, maybe it could even match orbits with the ISS for retrieval.
Or, much easier, just design the probe for eventual re-entry and parachute recovery.
I'll leave the exact delta-V requirements to smarter heads. I have no if the Vanguard orbit is even remotely in the same plane as the ISS (plane changes take mucho fuel).