Oh, good idea! Maybe you could even get something like a Zoom h1 you could ship to the person in question, if you want to get something good . very small and compact, and good audio quality, I hear. My zoom h4n is fantastic.
I imagine you could start the recording at both ends with a beep-tone, record the two people speaking in their respective rooms, and then use the beep-tone to "line up" the recordings and mix them. A net-friend of mine uses this tactic all the time to produce phone conversations for his radio shows; he's in Taipei and his correspondents are in Canada, the U.S., Sri Lanka, China, etc.
Heck, you could even use a clap, since 100% precise syncing wouldn't be absolutely necessary for an application like this. I sometimes do that when syncing video from a camera (or multiple cameras) to an audio track recorded externally.
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