Headphone cable with inbuilt crossfeed?

Would it be possible to construct a headphone cable with an embedded, simple, lightweight passive circuit that adds a calculated amount of crossfeed, with essentially no signal loss?
Somehow I think this could be very simple, just intuition. Might not be viable. (This is obviously just idealism, I know this can be done in DSP or with a circuit in the amp, but what I seek here is that this would work when plugged into any source)