Are you sure that reinterpret_cast is the right choice?
This is exactly the sort of thing that reinterpret cast is for. I use this technique all the time to pass object addresses to a window, in a message. I use reinterpret cast to convert the pointer back again to its real type at the receiving end.
"It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."
Richard P. Feynman