Bert is a seemingly itinerant man who works a variety of jobs, yet knows the magical Mary Poppins. What if neither Bert nor Mary Poppins are human? What if they're fay? Mary from the Seelie Court, and Bert from the Unseelie Court?
Focus on the bit from 1:25-2:14.
Or if you want to take it a step further, what if Bert is actually from the Shadowfell, and so thrilled to be in the Prime Material Plane that he's irrepressibly happy? Yet, like the clip above suggests, still haunted a bit by things he's seen... haunted and awed even...
I can't be the only one who's gotten some inspiration from Disney. What have you been inspired by? And bonus points if it's not one of the cartoons!