I posted my reply in the support ticket on the same subject. For convenience, I am pasting it below:
The aggregates can be configured through the DataSource Aggregates method and can be displayed with a ClientFooterTemplate(FooterTemplate in server binding mode) for the column. Please check the Aggregates demo for a sample. Multi column headers are not supported but a similar look can be achieved by prepending a row to the Grid header after it has been initialized. I created a small jsBin example that demonstrates this approach.
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