With BW 7.3, you can use the new 7.x dataflow for hierarchies and can use any BW object as the source (DSO, datasource etc).
- Have you tried creating a generic datasource in ECC, replicated, and then tried to create dataflow for the hierarchy in BW?
- You could also try using a DSO as your hierarchy source. You can create a generic datasource (master data or trans) to populate the DSO with your time dependent hierarchy data