Max as Ranuccio Farnese

My current painting project is a variation of Titian's portrait of Ranuccio Farnese, painted in 1542. Here's the original.

Titian, Ranuccio Farnese, 1542

I love the sensitive rendering of the boy's face and gesture, how he's a bit too small for his coat, and the gorgeous colors of his clothing. And, I think he looks a lot like my son, Max. So, for fun, I decided to copy this painting, but with the image flipped and the likeness of Max enhanced.
 
Here's how I started out on a large canvas. I rather like this sketch in its own right:
 

Julie Devine (work in progress), 2010

Here is the painting in its current state:
 

Julie Devine (work in progress), 2010

The shirt is so much fun to paint. I love the light effects in the silky fabric. In my next pass I'll also add more detail. I won't be taking it to the level of detail in the Titian - this will be a looser, more impressionistic take on the painting. The question is, can I get Max to sit for me for a few minutes? Unlikely!  I need the right incentive.