If you have Slic3r & Reptier, you can follow these steps
Slic3r:
A. Open STL
B. Rotate STL
C. Cut STL (you need to do it two times)
D. Stretch that require portion (as it is not having complex geometry, it shall work)
E. Save individual parts as STL
Start Repetier host
A load all three component
B. Place them. I use to edit X/Y/Z manually in terms of 3 decimal accuracy
C. Save it as STL
And if require, repair it using netfab.
I just edited NASA wrench and shortened the handle and added a PIN in similar way.
There is a web site that converts an STL into Openscad. Check on http://www.thingiverse.com/thing:62666. The result is not really user friendly, but this can help in some cases.
If you have not yet been able to complete this task, I will be happy to make the modification you need and send the updated version back to you, just message me on gchat!