pass multiple mdx member via ssrs drill through

I can use the following ssrs expression to pass a member in a ssrs drill through action

="[Geography].[Country].&[Australia]"

if I do the following

="[Geography].[Country].&[Australia],[Geography].[Country].&[Canada]"

This does not work.

There is a reason why I wish to do this, mainly because in my drillthrough report I am using nonempty in the parameter queries so if use =parameter.value as the ssrs expression for the drill through and one of the selected members is not available in the drill through is not available it won't work.

Regards