It is possible to re-use the oUF arena frames as preparation frames, but it will require some special handling as none of the elements will update correctly then.
I could add a system to handle this, then let the layouts just do the updating themselves. It would be similar to what Monolit does, but with the actual frames instead.
Callback would probably be something like:
Lua Code:
function(frame, id, spec, class)
end
Not really sure how sane this would be in practice.