Already a key player in subprime originations and securitization, Washington Mutual is launching a new conduit program that will buy mortgages on a bulk and flow basis. The new unit, which began bidding on pools last week, is expected to purchase some $5 billion in new subprime whole loan pools next year. According to reports, WaMu is targeting portfolios of 2-year ARMs totaling $50 million to $100 million from established subprime lenders. The conduit…