Hierarchical Roll-Up Fields for Campaigns

Hi all,

I would like to aggregate the number of qualified leads from all related campaigns to a "parent campaign".

The counting of all Leads to a campaign works well by using the roll-up field functionality.

But how can I aggregate all these information on the parent  campaign?

I've tried to use the hierachy in the roll-up fields. But it isn't available for campaigns.

Thanks for help and regards

Claudia