MDX Filtering And Grouping Data Within Subreports (help)

I have what at first site should be a simple reporting services issue but cannot resolve:-

I have a complex report comprising over 90 pages of various sections but when analysed in detail , 80% of it follows a simple pattern i.e. it comprises around 100 instances of the same sub-report bound to the same data source BUT grouped and filtered on different groupings and filter values.

The pattern is as follows:-


Each sub-report instance is bound to an SSAS cube which has fields L1, L2...L7

Each sub-report instance groups the data dynamically by one or more groups G1,G2..G7, the actual fields to be used being defined by the parent report (i.e. one instance may group by fields L7, L3, L4, another by L2,L3 etc)

Each sub-report instance has up to 7 filters defined (F1..F7) may filter the data i.e. the parent may pass a filter stipulating that L7="A", L3="B". To do this, the parent sets filter parameters F7="A" and F3="B"


The approach I have adopted is to set up parameters in the sub-report for dynamically grouping the data i.e. the
sub-report has 7 parameters defined G1..G7 and the parent report populates G1..G7 with the grouping breakdown required for any given instance. This works fine!!!!

However what I am trying to do is prevent each sub-report performing major round trips to the underlying cube for each sub-report instance by specifying the filter as part of the MDX query by defining the 7 filter parameters as query parameters. (I could of course not filter the query and place the filter in the report but this would almost certainly lead to performance issues). Instead what I am struggling to do is to create the MDX query in such a way that when a filter is not supplied by the parent, the MDX query does not filter the data.

Can anyone advise on this. I guess my question is more of an MDX question than a reporting services one.