So, draw order is generally layer based. So the top layers will draw over the lower layers. This also counts for the blocks that are inserted on certain layers.
The example model here shows how that works and I hope we can use it as an example of what you are trying to do.
Locking layers allows them to be visible, snappable but not selectable. In Display options locked objects can be automatically faded with color transparency and draw behind other objects. Would those settings work in this case?
Another way, but I am nto sure neccesary is Layer color can be changed to transparent colors. So potentially this could be used to fade out certain lines so they fade into the back, but still can be snapped to.
faded background.3dm (657.9 KB)