I don't believe there is a direct way of handling this, however, you could attempt to achieve a similar result with using the event-handlers on the input filters:
Using these filters, you can at least synchronize the filter-action to the datasource of the graphs.
Alternatively, you might want to consider avoiding the input filters directly, but instead using a page-wide filter using widgets such as combobox and other non-datagrid filters. You could in theory use these to create some filters, which then apply to both the datagrid2 and chart datasources. However, be wary of implementing such a method, since this will circumvent any optimizations done in the datagrid2 widget for optimizing network calls for fetching data.
Following your suggestion I assume I could use the filter widget events to recalculate non-persistant entities which the graphs can listen too. This coud surely work.
Is there a way avoid using the non-persistant entities? I mean, can I bind the graphs directly to the same entity listed and filtered in the datagrid2?