The credit general requirement requires a percentage of material recycled, and a formal report indicating how much was recycled and to what purpose. The detailed step by step guidance has an entry explaining what to do "If the waste management company separates, diverts, and disposes of construction waste" implying as I understand it that this method would be acceptable. However, steps to "Mark and designate containers. Have the waste management company provide separate containers for different types of waste based on its destination ..." and "... Sort and set aside, in a marked and designated area, lumber, plywood... " are also included making it a bit vague if offsite separation is a valid path to meet this credit. Any thoughts?
Your best bet is to have separate dumpsters for each of the main types of construction debris (wood, gyp board, metal, cardboard, etc.), however, the waste management company may do the separation of waste off-site. If waste is separated off-site, the waste company will need to show proof of the separation of waste from recycling and the final destination for each of the materials. (Off-site sorting gets more complicated and may become significantly harder to track.) As it states in the reference guide, facility "average" is NOT acceptable for documentation purposes and you will still need to show a site specific diversion rate to earn credit.
You may want to partner with local organizations who may come directly to the site to pick up certain recyclables.