Build your own Expression's

gistfile1.cs

var lam = Expression.Lambda<Func<string, bool>>
(
	Expression.Call
	(
		Expression.Invoke(
			Expression.Lambda
			(
				Expression.Call
				(
					paramExpr,
					typeof (String).GetMethod("ToLower", new Type[] {})
				),
				new List<ParameterExpression>{paramExpr}
			),
			new List<ParameterExpression>{paramExpr}
		),
		typeof(String).GetMethod("Contains", new [] { typeof(string) }),
		new Expression[]
		{
			Expression.Constant(query.ToLower())
		}
	),
	new List<ParameterExpression>{paramExpr}
);