Semi Additive measures - Poor performance issues

Hi,

I have created a cube. This cube is working fine except in case of semi-additive measure.

We are browsing cube in excel where if we select more than 5 measures it goes in to loop and we have to cancel the query.  We tried following to deal with this issue:

1) Created partitions

2) Created aggregations

3) Created 2 measure groups out of single fact table - one containing additive measure and other with semi-additive measure

4) Tried converting "LastNonEmpty" to "lastChild" where it gives blank results for all measures.

5) Tried firing MDX queries using same measures with no luck.

Note:

• We are working on SQL 2008 R2
• existing cube has 2 measure groups and 7 dimensions.
• Size of the cube is 30 GB 

Could you please let me know how can we improve the cube performance in this case.

Let me know if you have any questions or need additional information.

Thanks in advance for all your support.

- Prashant