This is currently not supported, primarily because feedback on our own framework actually suggested to get rid of the suffix, so we removed it.
It's an item in our tracker to add in the future (i.e. more flexibility to output naming, also namespaces etc.), currently it's not supported at this level.
You could rename the entities in the designer with the suffix 'Entity' but that likely gives odd names on the Context class. (you can do this in bulk btw, in the element search window, where you can write a small piece of C# to traverse the entities in the model and suffix the name)
One thing I wondered though: with namespaces, you could limit the conflicts though?