mhm this sound a bit like metaprogramming for me, you may inject a debugging method at runtime in your model, which will add the debugging statement just before the method call so you can inspect the call as needed, like:
m = MyModel.last
m.class.send(:define_method, :debug_my_method){debugger; my_method}
m.debug_my_method
this should do on the irb (just tested it on may rails console)