Is there a way to configure DrillThrough on a Virtual Cube without
granting access to the source cubes?

For example, let's say I have source cubes A and B. I build a virtual
cube, Cube V, and I create a role that only has access to this cube
(i.e. I don't want the users to see Cube A or Cube B). I configure
drill through on all three cubes. When I test the role, I get the
following error:

Unable to drill through. The operation requested failed due to
security problems.

If I grant access to the source cubes, it works fine but this defeats
the whole purpose of securing the cubes in the first place.

Does anyone know a way around this?