There are some Grooveshark methods that are not included in the Official API docs, but there are a few repos that document the Unofficial API and include these methods. The method you're looking for is getSongFromToken.
It requires country and token as parameters (token is "2IsoC7" in your case). You also need to set header.client to "htmlshark".
Here's a sample cURL request:
curl 'http://grooveshark.com/more.php?getSongFromToken' -H 'Content-Type: text/plain' --data-binary '{"header":{"client":"htmlshark","clientRevision":"20130520","uuid":"[YOUR-UUID]","session":"[YOUR-SESSION]","token":"[YOUR-SESSION-TOKEN]"},"method":"getSongFromToken","parameters":{"token":"fESpf","country":{"ID":223,"CC1":0,"CC2":0,"CC3":0,"CC4":1073741824,"DMA":534,"IPR":0}}}'
That should give you something looking like this:
"header": {
"session":"[YOUR-SESSION]",
"serviceVersion":"20100903",
"prefetchEnabled":true
},
"result": {
"SongID":"25134723",
"Name":"T4 Song",
"Flags":"0",
"EstimateDuration":"227",
"AlbumID":"3624474",
"AlbumName":"Sexplosive Locomotive",
"CoverArtFilename":"3624474.jpg",
"ArtistName":"Punish Yourself",
"ArtistID":"249162"
}
Unfortunately some of these variables are a little poorly named. token inside of header is your session token. token inside of parameters is the id of the song you're looking up.
Hope that helps!