I've got a couple of suggestions that might help.

One is to learn '3-note per string' scales.

http://guitartricks.com/tutorial.php?input=28

This will force you to use your pinky because there's no way to play them without using your pinky. Plus it will give you more to work with when it comes to improvising solos and expand your thinking a lot more.

Another suggestion is to delve a little into tapping to increase your pinky strength.

http://www.guitartricks.com/lesson.php?input=1873

Most of these exercises involve using your pinky very quickly and repetitively, so you should see a noticeable improvement in a very short period of time.