It’s not that IW is doing anything with the ImageMagic path. The plugin is just checking the existence of this extension and a number of it’s methods.
We’d rather say that 1&1 for some reason is forcing custom way of using the ImageMagic extension.
Unfortunatelly we’re not going to provide any hosting specific solution, even if we had 1&1 hosting available.
My suggestion is to switch hosting (sorry).