Hi Manu,
Can you try load master data to BPC from data-source without cube (chain /CPMB/LOAD_DATASRC_MDATTR or /CPMB/LOAD_DATASRC_MD) ?
If not I suggest you load data from your cube to the new BW info-object.
After that load master data from this info-object to BPC (chain /CPMB/IMPORT_IOBJ_MASTER)
or use this BW info-object as "external" in BPC.
Best regards,
Dmitry