Microsoft Report Builder - Full width summary row in a child group

Question

I have an SSRS report containing a parent and child row group. At present, this displays as:

I want to add a summary row to the "Child Group" but have it span the entire row. For example:

I also want the data for the "Parent Group" to repeat on every row whereas the data for the "Child Group" only appears once per value.

I'm migrating the report from another source, hence the odd requirements.

Thanks.