What seems to work is tweeting via private VPNs, running on anonymously-leased VPS. To route that VPN through Tor, you just run the VPN server (in TCP mode) on the VPS as an onion service.
But there's still the risk of cellphone re-verification. So for long-term accounts, you need a persistent number. One solution is to have trusted friends in other jurisdictions, who can activate the number for you when needed.