Not completely what you are talking about but the Dust Jet is a rear-mounted dust boot. Not having a shield on top that goes around the bit will somewhat limit the ability to contain the dust and chips, increase the effective suction and send them into the vacuum port.
What is needed is a force field that will contain all the dust and chips so there is nothing but a vacuum port! 
I think that there is a list of different dust boots in the Shapeoko Wiki and a quick search on Thingiverse will also show you a number of different designs.