Center based on chosen Key Points
The ability to align object to a key object is very useful, but it would be great if users could specify two key points and center a new object between them. For example, when you want an object to be centered between an existing object and the edge of a page, being able to say "Center this object between this point and this point".
Bastian S. commented
That is possible - select multiple objects and DONT set a key object. then it should work just fine.