A way to record the cost of native script objects

Currently there's no way to indicate the actual amount of memory consumed by native script objects (i.e. objects that wrap arbitrary data, such as Qt/C++ objects).
This can make the garbage collector unresponsive (not freeing objects as often as it should), because it doesn't know the real cost of all objects (since it doesn't know about the native data).
It would be nice if QtScript had an API for registering this cost, so that the GC can take it into account.