Note: the question has been radically re-written since this answer was written. Consequently, it is no longer relevant to the question.
If you want an object to stay between the Sun and Earth, it has to be at the Earth-Sun L1 point, which is about 1.5 million km away. We already have stuff there: https://en.wikipedia.org/wiki/Solar_and_Heliospheric_Observatory
At L1, you can arrange for your object to cross the Sun from the perspective of any point on Earth. However, this is different than casting a shadow on Earth. In order to cast a shadow, you'll need your object to have at least the same angular size as the Sun, as seem from Earth. Conveniently, the Moon has approximately the same angular size as the Sun, and it's only 384,400 km away. In order to have to be able to eclipse the sun from L1, your object will need to be substantially larger than the Moon.
Now that we're talking about something enormous, the physics of Lagrange points comes into play. They're only stable(-ish) for objects of negligible mass compared to the primary and secondary. SOHO has negligible mass compared to the Earth and the Sun. A sun-shade several times the diameter of the Moon probably doesn't. You could try making it a disc rather than a sphere (to keep its mass down), but I expect that tidal forces would spin it out of alignment quite quickly. Its mass will also noticeably affect Earth's orbit, changing the position of the Earth-Sun L1. You'll end up with a complicated gravitational dance as both Earth and your object try to share a similar orbit. Possible outcomes include:
- The object collides with Earth.
- The object collides with the Moon
- The Moon gets tugged into a much more elliptical orbit, resulting in far higher tides that make a giant mess on Earth.
- The Moon gets ejected from Earth orbit, possibly colliding with Earth.
- The object gets ejected into an elliptical orbit around the Sun, where it probably eventually collides with Earth, Venus, or Mars. Meanwhile, Earth ends up in a somewhat lower orbit and more elliptical orbit, throwing another big wrench into the climate.
- Some combination of the above catastrophes, which may involve the object being a temporary second moon for a while.