You can fork gossip and tweak it. In particular you'll have to fork nostr-types, edit src/types/url.rs and search for "is_global". Then you'll need your gossip Cargo.toml to use your local fork of nostr-types.
Discussion
oh, and you'll need to fork gossip-relay-picker just to make it use the same local fork of nostr-types otherwise rust will see them as different types. Then make gossip use your fork of gossip-relay-picker.