Hi,
Unfortunately, you will only be able to retrieve infopath data published as list's columns.
If you do not need to join your Infopath data with other SharePoint lists, you could possibly use the out-of-the-box XML data source for querying some aspx page of yours that would parse the XML data in your infopath forms and return some clean XML data ready to consume by the SSRS XML data source.
In the next version of Enesys RS Data Extension, we will also provide the ability to call some URL that return some XML data that can be converted into some dataset. However, because this feature will be provided as a new statement, it will be possible to join/merge/aggregate the resulting data with other SharePoint lists.
Hope this helps,
Regards,