The above theory holds consistant with what we know from non-canon material, in this case the Back to the Future Ride at Universal Studios.
Remember: "flux" means "flow" and "capacitor" means "temporary storage of change."
Consider this: the Delorean (and its onboard computers) know when the machine leaves the timestream (generally beginning in 1985 or thereabouts). When it travels to, say, 1955, the flux capacitor stores up the theoretical equivalent of thirty years and BAM two flaming tire treads later the machine is in the past. But what if the machine was designed to always return to its point of origin?
In the Ride at Universal Studios, Biff Tannen steals the Delorean and the crew in the ride have to bum his bumper and both machines return to their origin points. That would seem to mesh with that concept, but what's the link?
Theory: the flux capacitor is designed to store up time units equivalent to the difference between origin and current placement and as such, there exists (somewhere deep within the system) a means of always using the origin as a point of reference.
After all, "Jan. 1, 0000" means nothing in the timestream, but "2000 years ago" when "year=x" might be plausible.
So the flux capacitor makes time travel possible by using the origin point as a point of reference to translate what the driver wants into something that the universe can understand.