Easy way to calculate percentile in SSAS

Hi,

I have created SSAS database. I have almost 1 million of record for each measure . In a single MDX query i have to calculate 25th, 50th and 75th  percentile for almost 10 measures .

so Is there any way to calculate percentile which will provide better query execution performance  ?  or Do i need to make some changes in cube design ?

I would be appreciate for any help .

Thanks in advance !

Prashant Mhaske