If the little finger is what you primarily want to work on try something like:
l r m r l (l) m r l l m r ....
e |--4--3--2--------------3--4--5---/6--5--4-----
b |------------3--4-/5----------------------------
g |------------------------------------------------
d |------------------------------------------------
a |------------------------------------------------
e |------------------------------------------------

l = little
r = ring
m = middle
/ = slide

While you are playing this, vary the dynamics on each finger each time you play the riff (sometimes emphasize the little finger, others emphasize the ring, etc...). You can try to change the slides to bends, vibrato, or any other technique. Also, I added the ellipses (...'s) to mean that you can keep going up the neck in this pattern. Maybe you could try going all the way up to the 12th fret or, if you're feeling really adventurous, you can try to play it going up the strings (to the Low E string and back). Hope it helps ya.

David
-G101