For mirc 6.16 there exists an DLL to do this:

In mirc 6.17 this DLL doesn't work, the lines echoed through it don't appear anywehere, which makes this version useless for me since i show notices from network services in the active window on this way.

Are there any plans to add a function in a newer mirc version to get native support for that?
Not everyone wants multiple spaces to be eaten...