lookup function with aggregations in expressions

Hi,

I have 2 procedures which returns 2 result sets. These 2 procedures are my two datasets in the report and I use lookup function on a common field to read the related data from the other dataset. The requirement is when I do lookup DS1 with DS2 on common column column1, I will have to read column2 of DS2. The column2 returns multiple values for the lookup and I want to show these values as comma seperated in the tooltip of a chart which uses DS1.

Is it possible to do this in ssrs 2008 r2?

Please let me know if you know any way to do this..

Thanks,,

hmai