If i am correct, what you want to know is if there is a way to extend TaskManager via a plugin based approach( like Office/Ie/Outlook plugins).
The answer is no.
I however have a different approach which may help you do what you want but would be a lot more work.
What i suggest is Com interop based injection and override.
using Spy++ you can see what are the window classes/properties of the TaskManager window. Then you would need to write a program which works minimized(system tray?!) and watches for some identifying window/class name to pop up in the messages system. Windows messages can be intercepted and hooked. http://www.codeproject.com/Articles/33459/Spying-Window-Messages-from-the-Inside may be of some help.
Once you get your window handle. you will probably need to find the tabs control group. and inject a new tab element. Post which you can put anything which you deem into the tab element.
This is speculative, and involves the assumption that all the new changes you want to add would end up in a new tab.
I hope this helps you in some way.
PS: The answer is not totally speculative though. For some internal use at my workplace, I had made a prototype which would do something similar to outlook and override some default functionality which wasn't exposed by the Add in framework per se. Beware that this would require lots of testing and was somewhat unreliable/unstable