Select active working set with hotkey in Open Resource window

I am using Eclipse (PDT) for developing websites in PHP. As I have many projects, I use working sets intensely. Bes开发者_Python百科ides this one, another of the best features of Eclipse is Open Resource (Ctrl + Shift + R by default), which also supports using working sets.

However, in the Open Resource window I have to use the mouse to click on the little black arrow in the upper right corner to roll down the working set menu. Is there a way to do the same using the keyboard? Assign a hotkey or maybe already has one?

So that's CTRL+F10 and then the number of the working set in the list.