Can I use pkg protocol to download artifacts manually?

Julia now installs artifacts very quickly, with the help of pkg protocol. But if I want to install artifacts manually instead of intalling JLL wrappers, e.g. install an artifact as a build dependency (Clang.jl uses this to get multiple versions of GCC toolchain), pkg still goes to raw.github.usercontent to download it, which very slow in China. Can I do this with pkg protocol? I checked Pkg.jl and failed to find some internal API that does this.