Style/BlockDelimiters breaks natural language of rspec matchers

RSpec Expectations allow syntax like:

expect { ... some code ... }.to raise_error(MyErrorClass, my_error_message)

However if the code under test is not trivially short, it will need to be split onto multiple lines, e.g. here's some real-world code:

it "should barf if the definition's type is not right" do
  expect {
    fixture.definition = "sometype #{fixture.name} blah blah"
  }.to \
    raise_error(
      Pacemaker::CIBObject::TypeMismatch,
      "Expected #{object_type} type but loaded definition was type sometype"
    )
end

but this causes

Style/BlockDelimiters: Avoid using {...} for multi-line blocks.
https://github.com/bbatsov/ruby-style-guide#single-line-blocks

complaints from rubocop.

The problem is that changing it to

expect do
  ... some code ...
end.to raise_error(MyErrorClass, my_error_message)

completely ruins the previously natural language flow of the "expect ... to" statement. So what's the solution?

A related problem is that I'm also struggling to find a combination of line breaks/continuations and indentation which looks good here. Suggestions very welcome.

Review the RSpec Expectations examples and the Style/BlockDelimiters complaint in this issue, then read the comment thread for any agreed direction. A completed change would document a clear recommendation for formatting multi-line matcher expectations without losing the natural "expect ... to" flow.