What you are trying to do is bad practice, it doesn't matter that a detail fills the page nicely, it has to be to an acceptable industry scale 1:1 1:2 1:10 etc. using a scale of 0.4638 just because it fills the page nicely, is BAD CAD. Really bad. If it looks strange then try positioning the detail differently maybe add a second detail onto the same layout, or position notes around the detail to fill a bit of the empty space or use some kind of border around the detail with a scale and description to make it visually more acceptable. But what you are asking is a bad practice and you should forget it before it becomes a bad habit.
This is the reason why you cannot select annotations for those types of sizes. (Yes you could create them but you would need to create new annotation scales for every drawing you ever create) is that something you really want to spend your time doing?
