This is an idea for a setting in the editor that would allow you to place objects without any regard for the grid. Basically, you can place an object anywhere on the map, centered on wherever you click. It'll locate the nearest tile and place the object on that tile, and then it'll adjust the object's pixel offsets to compensate and position the object where you actually want it.
Of course, that would require that the map editor first recognize object pixel offsets to begin with...
Just a thought.
The v.455 map editor recognizes pixel offsets and lets you "nudge" objects into place. However, your idea is probably a nicer way to do things. We'll give it some thought.