You mean invoke a method expression or get/set the value of a value expression? If so it is possible. You need the javax.el.ELContext and the javax.el.ExpressionFactory. Both can be obtained from the FacesContext. Then call createMethodExpression() or createValueExpression() on the ExpressionFactory.
It is trickier if you don't have a FacesContext, i.e. outside a JSF request, but it is still very possible.
I'd be happy to provide you with more details.