Antlr 2.7.6 grammar inheritance combined with class inheritance

I am trying to extend a grammar by using Antlr grammar inheritance. The
class I am trying to extend has a rich set of ANTLR rules as well as
non-ANTLR C++ methods. Ideally I would like to inherit non-ANTLR
methods and override some of them (have my CPP class derive from
superclass). At the same time I would like to preserve ANTLR support
for grammar inheritance.
Now, seems like classDef antlr rule does not allow for that. One can
either do grammar inheritance:

class MySubClassTreeParser extends SuperclassTreeParser;

or C++ inheritance:

class MySubClassTreeParser extends TreeParser("SuperclassTreeParser");

but not both. If I have

class MySubClassTreeParser extends
SuperclassTreeParser("SuperclassTreeParser");

I get:

ANTLR Parser Generator Version 2.7.6 (2005-12-22) 1989-2005
..\expandedrewrite_query_oracle.g:13:39: rule classDef trapped:
..\expandedrewrite_query_oracle.g:13:39: expecting "Parser", found '('
error: aborting grammar 'unknown grammar' due to errors
Exiting due to errors.

Thanks in advance.

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