Hi Manuel
You can only pick this when you add a user to the list (unfortunately):
Embedded isn't an option though in here. I'm using HTML which comes as an attachment.
1829914 - Customize EWA Reports
It's not the intention that customers change EWA reports (see above SAP note) as SAP delivers how these reports look like ~ standard report delivered by SAP.
SLR could be an option but it's also pretty much restricted to simple queries in case the standard blocks don't suffice.
You could leverage data stored in BI of SolMan (of separate BI) to create your own custom report ~ probably most interesting if you've got a BI Suite License so you can leverage BusinessObjects products for reporting.
Kind regards
Tom