I know this is an old topic, but just in case anyone is still looking at this, as I was, I found the best option for me was to create a read-only boolean field in the table that comprises the data in my embedded list. I called my field "active." I then created a before delete business rule that prevents deletion of the given record when the record's "active" field is true (and allows for its deletion when the record's "active" field is false). I then controlled how that value is set from other business rules.
This doesn't hide the red "X" from appearing in the embedded list; however, it prevents users from deleting the records when they should be deleted in another manner, only after certain logical requirements are set.
This saved me from having to create a bunch of ACLs or add a bunch of on-the-fly data to the user's session through display business rules and constantly having to change it back-and-forth (and praying they don't have multiple windows open).
