I remember when Peter Wolf started up a blue grass band and played a bunch of J Geils tunes with them so this is not a completely original idea,

His name is Keller Williams and his band is called the Hillbenders.  I was pointed to this curiosity by the Vindicator from Youngstown Ohio.  The Petty Grass Band will be playing in Kent. According to the band leader Williams:

“Luckily, the Hillbenders share my passion for this music and it just so happens that they are [great] pickers who have amazing attention to detail. These Petty songs lend themselves quite easily to bluegrass and by the end of the night, the audience will more than likely be singing in harmony.”

I could see that being true about knowing all the lyrics, that does make it more fun for most people when they listen to music.  And you certainly can call their renditions sleepy.