Question might sound impossible but I'm still serious. Downloaded a plugin for firefox called "Modify Headers" (https://addons.mozilla.org/de/firefox/addon/modify-headers/).
Set it up like that:
Select Action: Add
Header Name: X-Forwarded-For
Value: Enter any IP address here.
Add this and press start.
Now go to https://www.iplocation.net/find-ip-address or some other site and you will see that your original ip has changed without the use of proxy.
However, this doesn't work on all / many sites, but still, maybe there is a better way doing this so it works on all sites?