You can use the gripmaster, just don't over use it. It will help get you pinky in shape, but its not the best way to do it. The best way is the 1234 exercise someone mentioned here before. Just go 1-2-3-4 on each string. Go from 6 to 1 then 1 to 6. Up and down strokes. Keep doing that, it builds speed and strength. For streching use:
e---------------------------------------------------------3-h-5-h-7--|
b----------------------------------------------3-h-5-h-7-------------|
g-----------------------------------4-h-5-h-7------------------------|
d------------------------4-h-5-h-7-----------------------------------|
a-------------3-h-5-h-7----------------------------------------------|
E--3-h-5-h-7---------------------------------------------------------|

Do that then go down in scale.