In the Perl-hash-wraps-C-struct setup, an object looks like {foo => 'bar', ... '__cptr' => \2131231231}. Well, with- or without the scalar reference to the number-that-is-a-pointer

What you can do to make the XS methods work appropriately on this construct while being able to store stuff regularly from Perl as well, is to define a typemap that will a) check it got a hashref b) check that the class inherits from your package, c) fetch the __cptr slot of your hash-object, d) check it's a scalar ref, e) use the integer as a pointer, f) cast that into your C type. b), d), e), f) are done in T_PTROBJ already. This would allow you to write XS like with T_PTROBJ. The only downside is that you'd lose the ability to access the outer hash from XS.