Placeholder Aaron Laffey is due to start Tuesday at Colorado, but the Mets believe they can get Shaun Marcum ready to be activated from the disabled list relatively quickly. Marcum, who has experienced shoulder and neck pain that required injections to ease, is due to throw two innings in a simulated game in a couple of days. Mets officials plan to have him ramp up to five innings, potentially in an official rehab game with St. Lucie in the Florida State League, in the next outing. After that, DL activation is possible.