Good question: you need an open relay for that, this currently is the only easy way to "infiltrate" the web of trust. There are other possible solutions, such as whitelist notes with some PoW, or create an invite mechanism, but they all require some form of agreement by the clients. By the way this is a limit of all WoT relays. I'm planning to make the WoT check optional and add other filters (keywords, pow, nip-05). This should help to have a more flexible configuration, still keeping a good amount of protection.