It is on our todolist and actually one of the things we are working on as we speak.
It will probably end up as a “New Layer with Clone Structure” menu item. Or something like that. There’s already a similar menuitem in the Paint menu (even though it is greyed out/disabled because it is not implemented yet).
To help you right now, remember, in a new layer, you can drag down a lot of clones to correspond to the length of your existing layer – and then go through it hitting your * key (“Clear Drawing”) each time you need an empty drawing.