Create a new bitcoin wallet offline with a website like this one
Transfer the amount you want to give to your friend to this new
Write the private key on a paper and give it to him then explain that since you have created his wallet he is not the real owner and tell him to do step 1 and 2 by himself if he want to really ...
Both are quite easily done. Selling and buying bitcoin, straight from a hardware wallet, can be done at the so called 'fiatgateways' such as www.satos.nl (dutch), I believe Changelly deals with the same strategy. You simply open an sellorder and simply send the amount you have set to sell to the walletadres (straight from your ledger) given by the ...
Using a prepaid card (if it's anonymous) is not something widely accepted, because it's not possible to see who's the sender. That's one of the main reasons to have some struggles.
If you have a bank account in Greece, you can easily buy Bitcoin using bank transfer (SEPA).