Build Boost (using b2) on Windows, but /MTd instead of /MDd?

I'm building Boost 1.72 on Windows, as part of a product build. I'm trying to build everything /MTd and, except for Boost, I've been successful. Unfortunately, though I've added "link=static" to the b2 command line, b2 insists upon building /MDd. Does anyone have any ideas on how to persuade b2 to build debug/static, rather than debug/dynamic?