Relocating an Acer platanoides 'Crimson Sentry'

I planted a Acer platanoides 'Crimson Sentry' in the corner of the garden about 4 years ago without really thinking about the light (or lack of it) with the result that even in the height of summer, I have a dark hole in the corner of the garden where this tree is because the colour of it just sucks the light away.  Over the last four years, its only grown about 10 feet (it was probably about 5 foot when I got it).  This year, I've taken the difficult decision to take it out and replace with a plant that is much 'brighter' to bring a bit of light to the corner of the garden.  I'm resigned to the fact that in digging it up, it will probably put it under so much stress that it will probably kill it, but if there was a chance of saving it, what would be the best way?  I'm thinking the roots might not have gone that far, so how much root ball should I try and dig up to try and keep it safe and relocate it.