As far as I'm aware of, there is no way of opening ports at an Internet CafÃ© or most public Wi-Fi access points. Virtually all public Wi-Fi access points use a NAT to allow all computers on the network to access the Internet through a single public IP. Most, if not all, will have some sort of firewall in place to block incoming connections and in many cases I've seen, some also block all outgoing ports apart the common ones such as for HTTP, FTP and E-mail.
As many Internet CafÃ©'s offer public Wi-Fi access by simply sharing out their existing Internet connection, if they did offer port mapping for its users, all it would take would be two to three people with active transfers from a P2P network for the Internet at the place to become virtually unusable for browsing. I'm sure if you've downloaded some large files from P2P, you would have found browsing the Internet quite sluggish until the transfers completed or were cancelled.
As far as I'm aware of, the only way one can get a public IP address on the move is through a 3G wireless broadband provider, however, they usually charge more per month than regular fixed point providers and have a small monthly quota allowance. If you do decide to subscribe to a 3G broadband provider to download from file sharing networks on the move, I would recommend speaking with the provider first to ensure their 3G data service offers a public IP.