I figured it out for this case.

They weren't actually using any flex code at all. All they were using was a namespace that was not even required. I just removed the include and deleted all references to the mx_internal namespace and now the class works great!

Very cool! Now I can send full objects from php to flash with extremely little effort. Whole database results just urlencoded and serialized to be sent back as text and then be re-created in flash with one line of code as a native flash object. Wonderful!