guys this night we (actually mth is the guy to get the credits) made a breakthrough !!! we have succesfully made a patch to an unbricker tool which lets you burn any hxf file to the dingoo's. The checks for unauthorized screens were all in resource files which are availible in the unbricker tool. 

we also found the the (unauthorized) image back in 2 files : http://users.telenet.be/IMS/Image1.jpg

give the offset known in those files we knew where in memory it would be, and I dissasembled the code using ida pro. MTH then took some time to look at it and he found the code wich displayed the image which led him to a conditional jump that just had to be replaced with a nop command.  

I then applied this same patch to an unbricker tool and let Evildragon (from the gp2x scene) test it out and he had succesfully burned one of the bricked units without haveing a Unauthorzed image poping up !

if someone likes to try it out on your bricked unit :
the patched test version is availible here : http://dl.openhandhelds.org/cgi-bin/dingoo.cgi?0,0,0,0,15,256

use it with an ILLI331.dl file from one of the other unbricker tool and for example the a320.hxf from firmware 1.20 !

also when testing follow these rules :
1) use windows xp (the usbtool method still doesn't fully work for linux users)
2) remove any driver you had previously installed for it (rockbox usbboot driver (for installing dingux), usb_boot driver from ingenic, etc) you can do this while putting the device in usb boot mode (holding B) and hooking it up to the pc remove driver in device manager from windows and reset the device, keep repeating step 3 till no more drivers are installed and windows comes asking for new drivers
3) install the drivers from inside the zip package
4) use the patched flasher to flash firmware 1.20 
5) go say thanks to mth on #dingoonity !

a few notes : the drivers DO NOT work on any 64 bit system, if you really need to you can use vmware to make it work (thats what i did) , if you messed up your nand a lot you can use usb_boot.exe to do a nand erase (be carefull with this) and try flashing again.

 
big kudo's to mth it wouldn't have been possible without him, after all he found the offset to patch and looked at the assembly code ! 
i learned a lot tonight 