Problem:
Your corporate organizational structure creates silos that prevent collaboration between people who may work on similar items or have similar interests.
Solution:
Does your boss care what you eat for lunch? Does he or she care who you eat with?
If the answer is ‘no’, then schedule a lunchtime forum and invite all the people you want to collaborate with. Create flyers, send them to multiple email distribution lists, make it look like a big initiative. Tell everyone to bring their own lunch and that you’re going to discuss a particular topic. Don’t stress out about a polished presentation, the main point is to get to know people’s names.
You could even just show up and say, “I just wanted to get your thoughts on this particular subject.” Or, “I know we’re in different organizations, but I thought it would be beneficial for us to know each other and share what we’re working on so we can help each other out if we need to.”
You can figure out what will work best in your situation. And you don’t have to ask permission because your boss doesn’t care what you do during lunch, right? If it’s beneficial and actually improves things, what boss wouldn’t want you to do that?
Breaking artificial boundaries is easy, especially since they are artificial.
grootship 
Congrats on starting grootship. Corporations, especially the bigger ones, may appear frozen rigid, yet most people in them appreciate the lateral thinkers and doers who innovate and add new value.
Not breaking any rules, just testing elasticity. (BBS tagline, ca. 1988)
Yes, testing the elasticity and lateral thinking are good descriptors of grootship.
Thanks for your support, Bernd.