Correspondence with Purkey in 2001 is quoted here. He said the original version was:

You've gotta' dance like there's nobody watching,
Love like you'll never be hurt.
Sing like there's nobody listening,
And live like it's heaven on earth.
(And speak from the heart to be heard.)

Another variation (there are many out there):

Work like you don't need the money
dance like no one is watching
sing like no one is listening
love like you've never been hurt
and live life every day as if it were your last