Unfortunately, you can't catch rvalues of a move-emulation-enabled type in a deduced context as you've tried to above (in C++03). If you want some ideas on how to get something like this to work, search the Boost developer list under the messages subject "[boost] [move] new rvalue reference emulation".
The easiest solution, though, is simply to split the construction into two steps:
clone_ptr<D> d = makeD(); clone_ptr<B> b = boost::move(d);
(This still requires the additional constructor you've given above!) I *think*, due to RVO, there shouldn't be any overhead with the above pair of statements compared with rolling everything into a single statement.
If this doesn't fulfill your needs, I suggest reading through the thread given above in the Boost developer list.
Thanks a lot for your answer, reading into the source you suggested now. It is a serious drawback of move emulation tho imho as pointer upcasting is rater basic (smart) pointer related stuff. Time to update a compiler I guess ;) Cheers! Simon