Just because there are sites that suppor the functionality
doesn't mean there's a publicly available solution.
I would guess (and I"m just guessing here) that if the sites
you mentioned are using FCS/FMS to handle the recording, they have
also made their own deals with Nellymoser for the codec and
developed their own server application to handle the conversion.
Perhaps you might try contacting them to see if they'll give you
some insight as to how it was achieved.
If you do get in touch with them, you might ask them what the
magic word is to get the Nellymoser people to answer an
email.