Gravity launches are a common and approved by aviation authorities method at the Bezmiechowa Gliderport in south-eastern Poland:

https://www.youtube.com/watch?v=YHWcXja9C1s
https://www.youtube.com/watch?v=bdHNRok6Dtk
etc.

I did it there in my (then) SZD-55 standard class modern ship, and could easily continue with an extended ridge flying. Great and costs next to nothing.

BravoMike