Hi, I came across the following when looking up the net for info on E Flat Clarinets. It was at the end of a talk by Andrew Roberts, Chairman for the Clarinet & Saxophone Society of Great Britain.
http://www.theclarinet.co.uk/articles/eflat.shtml
He concludes ~
"My personal exercise for the Eflat consists of playing as much of the time as possible in the upper register without the register key. This forces you to use the correct air speed and helps create a true legato. Try it on the clarinet too, you will be amazed how much it can improve your playing."
So I have tried it on the Clarinet. First I play a note in the upper reg with the key and then release the key and play as many notes as possible without loosing the embouchure until it dwindles. It works. I reckon with more practice I will get a lot more out of it.