jbaldy, I wasn’t really addressing Rav Belsky’s position on this specifically. I am speaking generally on this issue. Other rabbonim have paskened it is only an issue if there was a possible intent to have otherwise made a purchase; otherwise not.
In the case of the OP here my point is even stronger. He wasn’t looking to make a purchase. He happened to hear a song on the radio that he liked. The station made the song freely available for download, presumably within legal fair use copyright limitations (otherwise they’d have their pants sued off — although non-Jewish copyright law doesn’t have a role in halacha as dinei mamanos [for non contractual transactions] do not fall under the rubric of dinei dmalchusa). And the OP is simply splitting a song off a track he already has legally downloaded, that he wouldn’t have purchased and only downloaded once he heard it on the station, and all he is doing is making one file into five files.