Why not use the ever decreasing costs of space flight to lift blocks or reflectors into our planetary L1 point? We wouldn't have to affect our own atmosphere to do this, though it may cost more to get a sufficiently sized object into orbit.
The good thing is that, when it's no longer needed, it can use those same attitude control sails to go towards the Sun-Venus L1 to start cooling down our sister planet.
I have the impression it'll take a long time to get rid of the rotten egg smell, but, if it's cool enough, we can hope to fixate some of the carbon in the atmosphere and cool it even further.