If our CAN-SPAM act can't do it, the Security and Exchange Commission can. According to Inside BA (via Security news portal), the SEC already suspended 35 companies which resorted to the stock spam campaign:

"The SEC said it took the action to protect investors from fraud, because the accuracy of information in e-mails about the companies was questionable. The SEC did not identify who had sent the e-mails or say whether any of the companies was responsible.
The suspensions are part of an SEC effort called "Operation Spamalot," which began last fall. The suspensions will last for 10 business days, through March 21."

Right on baby! If you can't hurt the spammers (although SEC swears to be going after them too), the people and companies buying their services can surely be slapped on the wrist.