If you have a DVD burner and the right software you can make a copy which has subtitles. Of course you would also need the dialogue in a text document. Strictly speaking this would not be legal. However, if the producers won't include subtitles on the official release they would find it difficult to prosecute a person who made a subtitled copy for a non-British or deaf friend. Particularly if the friend had also purchased a copy of the original DVD.
Just a thought.