Combine data from SAP BW and relational-universe

Hello,

We want to combine data from a SAP BW query and a relational universe in a WebI-report. Basically that works with merged dimensions, but:

Obviously it's not possible to use the function "result from another query"in the query filters pane, which I would need. Retrieving all SAP BW data would take too long, as it contains a huge amount of data.

Any idea how to overcome that?

Another approach would be to combine the data using data federation. But the multidimensional structure gets flattned and gets also too slow.

Thanks for your ideas!