Hit it with a BIG icy comet
It will cause what is called impact erosion on the atmosphere.
Impact Erosion
One outcome of a very large impact is known as impact erosion, which results in the loss of atmosphere due to hypervelocity expansion of a vapor plume from the impact; in other words, the impact literally blows off some of the atmosphere to space. There are two basic requirements for impact erosion to occur. The first is that the impactor must strike at a velocity high enough to form a vapor plume that will expand at a speed greater than the planet’s escape velocity. The second is that the mass of the vapor plume exceeds the mass of atmosphere above the plane tangent to the impact. (i.e., everything from the horizon upward). A rough estimate of the mass of vapor created during an impact is given by
Mv = (0.4 vi2 Mp) / ev(6)
Mv is the mass of vapor
vi is the impact velocity
Mp is the impactor mass
ev is the specific energy of vaporization of silicate rocks (5.7 x 107 J/kg)
The estimated minimum impactor mass for impact erosion is 4 x 1015 kg, and the estimated minimum velocity is 25,000 m/s.
Impact erosion probably played a significant role in the early history of planetary atmospheres. Repeated bombardment by large impactors would have certainly resulted in the loss of some atmosphere.
I imagine something like a 20km Comet would do the trick of knocking a lot of those greenhouse gases out into space. After a decade or so Venus would likely settle down and we could see what we've done.
Couldn't be less habitable after that than it is now.