Use locally installed Rust toolchain rather than fetching

I'm using rules_rust with code that I'm also compiling with Cargo directly. I'd like the versions to match between what I'm doing inside and outside of Bazel. The easiest way to do that would be for rules_rust to use my locally installed tools (that I'm already managing directly) instead of having to manually match the versions myself.

Is there a knob for telling the rules to pick up the installed Rust toolchain rather than fetching one?