How to use a custom stemmer from Python bindings?

Hi,

I'm using Xapian bindings for Python in my project. How could I use a
custom stemmer instead of the included one (Snowball)? The one I'm
looking at right now is Hunspell (http://hunspell.sourceforge.net/)
which has Python bindings (http://code.google.com/p/pyhunspell/).

Thanks in advance,

Eugene