[XorNot]

I do wonder if some of the "massed solar sail" ideas for terraforming Mars' atmosphere would work here (in short: use cellphone processors to build and launch a couple hundred thousand solar-sail equipped satellites).

Because it would be expensive, but it would kill several birds with one stone: we (1) prove whether the concept would work on Mars, (2) develop the technology to do it, and (3) unlike SO2 in the atmosphere, "switching it off" or modifying the scale of the effect can be done almost instantly (you could remove the swarm by having it fall back to an Earth orbit).