[boost] [type_erasure] How to have just one behavior from relaxed without inheriting the other behaviors

Hello, I need to create a type_erasure::any with just this behavior from relaxed: copy assignment of any uses the copy constructor if it can't use assignable(either because assignable is missing, or because the stored types do not match). But without adding the other behaviors, is there a way to implement this? Regards, -- Felipe Magno de Almeida