And.... FIXED!
There was no way I could stop UBoot, I have no idea why but I tried everything, even 2 different RS232 TTL interfaces. So I realized I had to work with what they offered me, the CE loader menu. One thing caught my attention:
d) Download from platform builder nowHmm, I don't have platform builder, I wonder what it does. Wireshark to the rescue - it looks like TFTP on a non-standard port (980). Well, I could of course code something together but am I the first one to look at this? Apparently not, because a quick google found CELoader, which is a standalone program (oh wait, app these days) to do exactly that, offer an NK.BIN to anything asking. Only source code, well I can do that. So I built the CELoader.exe, extracted the NK.BIN.COMP from the 2.35 cab, decompressed it to NK.BIN and put it in the CELoader.exe folder. Started CELoader, halted the scope on the CE loader menu and pressed <d>. It works.... well, sort of. The scope hangs on the splash screen but the RS232 is not flooded with error messages this time, so who knows? Fired up PuTTY and yes, we have a telnet connection. The rest is simple, there where 2 .lnk files in Secure\Startup, one infiniivision.lnk and one infiniivision_ext.lnk. Why? You tell me. Renamed infiniivision_ext.lnk to infiniivision_ext.xxx and rebooted the scope. Bingo! That's enough for this evening, I'll try the -l all -l bw50 tomorrow
Thanks for all the comments, specially from memset who made me not give up and admit defeat.