その名も、stub_chain
subject.stub_chain("one.two.three").and_return(:four)
(参考)
https://www.relishapp.com/rspec/rspec-mocks/v/2-0/docs/stubs/stub-a-chain-of-methods
mockと組み合わせるとこんな感じ
mmock = mock
subject.stub_chain("one.two.three").and_return(mmock.as_null_object).should_receive(:hogehoge)