(adsbygoogle = window.adsbygoogle || []).push({}); 1) Bypass the update to login to the PSN in the regular way, using PSProxy.
2) Visit the PSStore and add the game you want to your downloads.
3) Eventually the download will fail, but that's fine.
4) Stop using the proxy to bypass the system update by editing your network settings.
5) Retry to download the game, this time it will download it successfully. Remember to not install the system update during this step!
6) Once the download is finished and the game installed, you can start it and/or go back to using PSProxy again.

Note:
While this worked for FIFA17 Demo, the Spotify update for example could not be installed without updating my system. I have yet to test if you can or cannot apply game updates in general.

says connection to server lost when trying to download without prozxy on

EDIT::: Make sure you go into ps4 network settings and turn proxy server off and it will begin download!

Yes that's what I meant, I should have specified that in step 4.
Edited OT

i am signed in and the download is working but it say "can't install"

That is probably because the latest version of your game is supposed to only run on the latest firmware, there is nothing you can do about that other than upgrading