Success! been using my remote for several days now with my pioneer head unit!
This is the schematic of the original joystick.
Your headunit must have wired remote control input for this to work! Notice the stereo jack marked W/R on the back near the aux input!

This is the schematic of the joystick.
The joystick can be taken apart easily. Just unhook four plastic hooks and you can see the inside. Nothing will pop out and get lost. Take pictures of the inside before proseeding with removing the cirqit board! they'll help you out when assembling everything back together.
This is what the joystick looks like without its cap.
This is the cirqit board that we will be moding.
Carefully solder off theoriginal SMD resistors from the board. (I heated one end of the smd with a very thin soldering iron and lifted it carefully. then heated the other end until the three of them came off). Use a multimeter and start measuring (yes i suppose you know how to use a multimeter and follow the lines of a cirquit board?) You'll have to solder a cable for every function! So when you press a button on the remote you should have contact between the leads marked as <общ> or <general, common> and the <pressed function's lead> .
MEASURE Please! The folowing picture with all function cables is from a 206 so don't take it for granted! It's fully ilustrative of what you should have when finished soldering.
Anoter picture different joystick!
Assemble everything back together and you should have the joystick looking like this:
Make a small cirquit board if you want it beautiful or just solder the resistors with values according to the schematics given in he previous posts.
beautiful:

not so beautiful:
Use a stereo jack to connect the resistors to the headunit.
Thainks to: Peugeot club Bulgaria!