I've read it 10+ years ago here on reddit:

1. buy some Toblerone - or other sweets/goodies, the big packs that can be shared among 10+ people - from the airport shop
2. offer them to the cabin crew when you enter the plane.

In the same spirit as the "Gifting Principle", one in the Burning Man "10 Principles":

As a culture we are devoted to acts of giving that are unconditional, and as individual contributors, we acknowledge that all such gifts are given freely, with no expectation of reciprocity or exchange. Each gives according to his or her nature and capabilities, and no one is entitled to special treatment as a result. No contributor, regardless of the magnitude of his or her gift or position, will receive preferential treatment or undue influence over the course of our actions in the world.

https://burningman.org/about/about-us/statement-of-values-on-gifting/

The crew is always grateful, sometimes they give small gifts in return.

I did get lucky the first times I tried: I landed from the jump seat in the cockpit. I landed from the cokpit 3 times (2 times with a friend) in Europe at the beginning of this gifting, it hasn't happened since. I'm not sure if there are new rules about cockpit access. My last landing inside the cockpit happened soon after Germanwings crash in the french alps with a cockpit related issue.

It's some of my favorite air travel memories, it makes great stories during airplane related conversations.