need to link a structure to each anchor

I need, to program my browser to link any HTAnchor (child or parent) structure  
with a client specific structure, wich is in my case an Objective-C object id.

If the library was in Objective-C, i should have made a sub-class of the  
HTAnchor class, but that's not the case ;-).

For the moment, i've modified the HTAnchor.c module to manage one more field :  

I was wondering if anyone had as a better idea to do so.