Access prebuilt library when compiling with cpp plugin

I’m using the cpp plugin, and trying to compile/link against an existing (non-gradle built) prebuilt library on Windows. This user-story for the C++ support seems like it should support what I’m trying to do:

model {
    repositories {
        prebuilt {
            boost_regex {
                headers {
                    srcDir '../../libs/boost_1_55_0/boost'
                targetPlatforms "x86", "x64"
                binaries.all { binary ->
                    // Locate the exact boost binary required
                    if (binary.toolChain.visualCpp) {
                        outputFile = file("../../libs/boost_1_55_0/lib/libboost_regex-vc71-mt-d-1_34.lib")
                    } else {
                        outputFile = file("../../libs/boost_1_55_0/lib/libboost_regex-gcc71-mt-d-1_34.a")
sources.main.cpp.lib library: 'boost_regex'

But when I try to compile my library, I get the following exception from gradle:

> Exception thrown while executing model rule: model.repositories
   > Cannot create a ArtifactRepository named 'prebuilt' because this container does not support creating elements by name alone. Please specify which subtype of ArtifactRepository to create. Known subtypes are: PrebuiltLibraries

I’ve tried using “PrebuiltLibraries” in place of “prebuilts” but that doesn’t help.