I bought a B&M quickshift so we have the same problem in such way!
I realise that to remove the complete lever U will have to remove the box.. cause you can't access the clip to remove the axis which link the lever to the shift rod on the box...(which goes through the eye that u see on the lever's bottom)
As I want to upgrade my clutch with AP stuff it's juste a question of time for me but you may find easier to follow Spage's advice to replace the top part of the lever only.
Try to hold the base and kind of unscrew the lever to remove it but take care of not bend the linkage...