I have a yawl, and setting the mizzen at anchor, even half rolled up, keeps the boat straight up into the wind
all the time. (The mast
rotates in its round step socket and partner, so you furl sail vertically.)
This is probably somewhere between "impossible" and "more trouble than it's worth," but. . . . depending on the layout of your boat, you could add a small removable mizzenmast and removable boomkin. The mizzen is sprit-rigged, and with the sprit removed, the sail can be rolled down to half-size or nothing at all. If you're on a long passage
, you can pop the mast
and boomkin out entirely and stow them.
Mine is off the centerline of the boat, a foot or two to starboard -- to keep it out of the way of the outboard
-- and it functions just fine.
I know -- kinda off-the-wall boatbuilding/modification, but I figured I should throw it out there.