I had thought I read it somewhere, so I went back and checked. It definitely sounds possible from the .pdf, but on the main cd changer page it says:

Multi-Media X-Path Auxiliary Inputs - We have answered the call for a high fidelity way to feed audio into a factory radio. The Multi-Media Auxiliary input found on select Peripheral interfaces allows an auxiliary source, such as VCR, DVD, Game System, MiniDisc or MP3, to be routed directly into the factory radio through the CD Changer port. Note: Can only be utilized with aftermarket CD changer connected.

They should make this more clear in the .pdf file. My guess is that the adapter only interprets the signals between the changer and the hu, but if no changer is there, it can not emulate on its own. I dont know why someone would not make a simple box that would emulate the changer as simply as possible and only have aux inputs.