You can select multiple body parts at once and manipulate them. If you want to make a fist:

Drill down the Scene hierarchy until you see all the [finger]1 items.
Click on the first one.
Hold down the CTRL key and select each additional one.
Right click on the Bend option and enter a numberic value.

Now all of the fingers have bent the same amount. You can then click on the plus sign for each finger to reveal [finger]2, CTRL click each one, and bend them as well. (And of course, you can select [finger]1 and [finger]2 (etc.) at the same time if you want to bend them by the same amount.)

You can also move the slider around - it depends on what you're more comfortable with.