None of these other methods will work. Even a person with the strongest willpower might one day want to sell their Bitcoin. That's why if you want to hold your Bitcoin long-term, send it to the wallet of someone you trust and agree not to get it back before a certain period. Another alternative is to send it to an address you created, store the key on a flash drive and put that drive somewhere you can't easily access. After a certain period, you can go there and get it back.
There's no other way. If your Bitcoin is somewhere you can reach easily, there's always a chance you won't be able to resist selling it.
I think the time locking solution makes more sense than the rest, if there's a good platform where one can lock or stake their bitcoin for a certain period without being able to access it until the time frame they locked elapse then it would be more better an easy for investors to achieve their aim without selling, it would help the investors to reach their target of 5, 10 or 20 years, even more better than sending it to someone else's wallet, when it comes to money sometimes trust can be broken, the person can use your use money and come up with excuses when it's time to give it back. Anyways holding bitcoin for long-term is all about determination and when an investor is determined then they'll have the will power to achieve their aim.