Just make sure it's more than 300nm direct track between the airfields (even if your route is longer!), otherwise it won't be valid.
Another myth, I'm afraid. The requirement is to complete a flight of at least 300nm during which a full-stop landing is made at two aerodromes different from the aerodrome of departure. There is no requirement for the aerodromes to be any particular distance from each other. For example, Jersey - Guernsey - Alderney would be perfectly acceptable provided that you flew around the area enough to make the total distance exceed 300nm.