Indeed, we cut this from v3.0 because the model-first scenario was too complex to get it done on time, so we postponed it to a later v3.x version (3.1, 3.2 etc.) It will be added, it's not said when.
That said, in general one should strive for a domain model which is more fine grained than the tables it's mapped on. mapping an entity onto multiple tables does the opposite, so it might be you really shouldn't do this? (i.o.w.: you only really need this if the tables involved are all mandatory for an entity and you don't want to use inheritance (TPE). In general separate tables for an entity suggest 'optional' data, normalized out to a separate table.