Just to clarify, securities issuers would simply set themselves up as a Ripple gateway. They would issue a set number of security IOUs and take Bitcoins in return. Those IOUs could then be freely traded by the market, while the issuing gateway would be free to fund their projects using the Bitcoins that were received in return for the IOUs (shares/bonds) that they issued. Dividends would simply be paid as BTC to whoever happens to hold the IOUs for the given security.