Nothing allows you to broadcast to clients which are not monitoring the Message Queue while in the background.

Innerspace works because it places a layer between the program being loaded and the I/O Message Queue. It intercepts all communication between these 2 points and does with it what you program it to.

Its a little more in depth as to what exactly goes on, but suffice it to say that Innerspace can force applications to think they are the "Active" window and creates a separate Message Queue for each instance.

NOTE: Also, with Innerspace, no additional boxing software is necessary. You need Innerspace and the addon called ISBoxer.