Artifacts how-to exclude intermediate paths

My build process builds the target files in build_dir/bootfs/. I use:

artifact:
  - paths: build_dir/bootfs/*

The files in artifact.zip will extract to ../build_dir/bootfs/.

Is it possible to specify that the path leading up to the files being zipped is not to be included in the zipfile so that when I unzip the archive the files that were originally in build_dir/bootfs end up in the current directory?