The main problem in building a virtual extender is that you don't know the protocol. However in this case it was possible to build a proxy first so whatever it received it just passed onto a real extender. Then whatever the extender sent back the proxy sent to the remote. It's then just a matter of finding the patterns in the data stream and trying to figure out why some numbers change the way they do.
For example in every packet there is a packet counter that is used for resending of packets if they are lost on the way. So the virtual extender needs to keep track of that number and send the correct one back in all responses. This isn't hard it just takes quite a lot of time in comparing different binary dumps.

I still hope Philips releases a real virtual extender or as a second best option releases the protocol. If they only would do that we could build a much better virtual extender.