Hi Mah,
Maybe I wasn't clear in my previous post, you have 2 options:
1. use multi provider - you need to create a staging cube to match the one of the cube to the other, downside is duplicating records, upside is performance.
2. use virtual provider - downside is performance, you need to test this one and lots of ABAP, also beware of transport, upside is no duplication of data.
Andy