I notice all of the instructions are to rub the block on one's face. Is there a reason why one cannot rub the block on his hands then apply to face?
The Thai Crystal brand of deodorant stones, which are made of 100% Potash Alum according to one forum member's research as posted in this very thread, is also available in a liquid spray deodorant. It's perfectly clear and a good deodorant. I pay $6.95 for several ounces at the local natural foods store. It lasts a long while.
(I've only used it as a deodorant, but I imagine it would work as a post-shave splash too.)