Da untenstehender Tipp international interessnat ist, poste ich ihn auf Englisch.
The official way is this:
How do I get an invite? - Ingress Help.
It did not work for me ;)
I realized that two Googlers and Ingress/ Niantic people were giving out invites for people who showed some creativity in presenting the Ingress-Logo.
Now I am a total failiure if it comes to visual creativity. I thought about creatng the Ingress-Logo with sticks in grass or with ballpoint pens on my floor.
I put this in a post, tagging it with #ingress and mentioning +Jen Hsieh and +Brandon Badger, who were the ppl giving out accounts.
It took less than 30 Minutes to get the account. ;)
By now I also created a "Enlighened Bodensee Ingress"-Page on G+-