This strange advice was overheard at a bus stop by Jack Chandler. I believe this is a mash up of “fiddle while Rome burns” (to do nothing or something trivial while something disastrous is happening) and “sing for your supper” (to do something in order to receive something). Perhaps the speaker was thinking of the roaming violinist in some Italian restaurant or strolling strings at a banquet. For some reason the malaphor reminds me of that John Denver song, Thank God I’m a Country Boy:
Well I got me a fine wife, I got me ol’ fiddle
When the sun’s comin’ up I got cakes on the griddle
And life ain’t nothin’ but a funny funny riddle
Thank God I’m a country boy
Thanks to Jack Chandler for sending this one in.