Is it possible to mock a concrete class using EaskMock? If so, how do I do it?
Yes: http://easymock.org/EasyMock2_4_ClassExtension_Documentation.html
Powermock extends EasyMock and allows you to mock concrete types, even final and static methods.
PowerMock is a framework that extend other mock libraries such as EasyMock with more powerful capabilities. PowerMock uses a custom classloader and bytecode manipulation to enable mocking of static methods, constructors, final classes and methods, private methods, removal of static initializers and more.
When creating a mock, simply use the org.easymock.classextension version of the EasyMock class. The result will be castable.
Here's a recent link - http://easymock.org/EasyMock3_2_ClassExtension_Documentation.html
See the EasyMock Class Extension documentation and download it from the SourceForge project. You can't mock final methods though.
EDIT: This is now part of EasyMock for v3 and above, as noted in comments.
EasyMock class extensions have been integrated into EasyMock as of v3.0; see the release notes.