There are a couple of things you can do...
First, using an Jive App (which is an OpenSocial gadget), you can push in activities from Jive and pretty much wherever else you want. What you would do is use the app gateway to push in the activities. These would flow onto the activity stream. However, one really cool thing that you can do is use actions and notifications as well with embedded experiences. Check out the blog post I did on using What Matters to surface workflow: What Matters? Workflow! -- Use Jive's activity stream to surface multi-system workflow!
Let me know what you think! Happy to help you get going and building a killer app.