How to reference the protoc toolchain in rules

[newyankeecodeshop]

I am excited to take advantage of the prebuilt protoc compiler!
I have a sh_binary rule that uses protoc via a dependency on @com_google_protobuf//:protoc. What is the best way to replace the dependency so that I can use the prebuilt compiler from the shell script?
I assume it is to use a toolchain attribute on the sh_binary rule? I could not find the public name of the toolchain.
Thanks!