How does one extend the sound of the *daleth* in the *echod* of the *shema* as prescribed in [OC 61 (6)](http://www.hebrewbooks.org/pdfpager.aspx?req=14170&hilite=29c758ff-c40f-4d68-b7cf-40cac876d9fd&st=%u05d3%u05dc%u05d9%u05ea&pgnum=188)?. The letter as we say it does not seem to allow extension. See http://en.wikipedia.org/wiki/Dalet which defines it as a "a voiced alveolar plosive" and http://en.wikipedia.org/wiki/Voiced_alveolar_plosive which defines the last term.