OpenSSL in ruby: PKCS#8 format for private key

Question

I've created an RSA private key in ruby with:

require 'openssl'
key = OpenSSL::PKey::RSA.generate(1024)

I can get the key in PEM or DER formats:

key.to_pem
key.to_der

But there doesn't seem to be a way to get it into PKCS#8 format. The best I've come up with is to call out to openssl in another process:

require 'open3'
Open3.popen3('openssl pkcs8 -topk8 -inform PEM -outform PEM -passout pass:password') do |stdin,  stdout, stderr|
  stdin.write(key.to_pem)
  unless (err = stderr.read).empty? then raise err end
  stdout.read
end

There must be a better way that I just can't find. Does the OpenSSL class library in ruby have a mechanism for doing this?