managed to upload it via ssh with tftp, ( idea from @ironstorm
about svp. but seems theres no sftp-server installed etc, but found there is a tftp ... )
so no usb sticks, or y-cables etc needed
will give other people a guide here ...
1. You need a tftp server running, so get tftpd64 running and setup on ya pc (from here http://tftpd32.jounin.net/tftpd32_download.html
2. my chromecast worked as such, just wasnt able to actual cast anything, so use the proper google app to set it up on WiFi if it isnt already
3. get chromecast into recovery, power up/down/up/down seems to induce it ! not sure like ironstorm what the proper procedure is !
4. then connect to it via SSH, i used PuTTY (ip will be different than when you initially set it up on Wifi with app)
5. then in PuTTY once connected /user/bin/tftp -g -f eureka_image.zip 192.168.x.x
6. then flash-image eureka_image.zip
7. once its finished ! .. reboot (powercycle)
and wahoo ! working chromecast again !!!
just to note, as i was worried .. althou we have no SSH etc when its running as norm.
we DO have SSH while in recovery/flashcast as above, it doesn't remove that, so its all good for next update, which can be done via this procedure too