Bendingiscool has the best idea....

You need to create 2 render layers, one with the single object and your HDRI sphere (if you need the other two relections add them also but have only visible in reflections) and the other render layer with the other objects and if you need the first object in it just for reflection you can turn off it's visibility and have it visible in reflections only.
Save the renders out on the format that allows an Alpha channel and then composite the two renders together in something like Photoshop.