There is now a module in the Apache trunk called mod_proxy_wstunnel which allows mod_proxy (ProxyPass/ProxyPassReverse) to pass through WebSocket traffic. Someone wrote a blog post about back-porting mod_proxy_wstunnel to Apache 2.4/2.2 and provided a patch to do so.
I figured out concrete instructions to set up mod_proxy_wstunnel on Ubuntu (tested with Ubuntu Server 11.10 and Apache 2.2.20) and posted them on my blog. I have copied them below:
# Check apache version (should be 2.2.20 as of writing, if not adjust the next step)
dpkg -s apache2
# Checkout apache source
svn checkout http://svn.apache.org/repos/asf/httpd/httpd/tags/2.2.20/ httpd-2.2.20
# Get patch and apply it
wget http://cafarelli.fr/gentoo/apache-2.2.24-wstunnel.patch
cd httpd-2.2.20
patch -p1 < ../apache-2.2.24-wstunnel.patch
# Build Apache
svn co http://svn.apache.org/repos/asf/apr/apr/branches/1.4.x srclib/apr
svn co http://svn.apache.org/repos/asf/apr/apr-util/branches/1.3.x srclib/apr-util
./buildconf
./configure --enable-proxy=shared --enable-proxy_wstunnel=shared
make
# Copy the module and recompiled mod_proxy (for new symbols) to the ubuntu apache installation and update the permissions to match the other modules
sudo cp modules/proxy/.libs/mod_proxy{_wstunnel,}.so /usr/lib/apache2/modules/
sudo chmod 644 /usr/lib/apache2/modules/mod_proxy{_wstunnel,}.so
echo -e "# Depends: proxy\nLoadModule proxy_wstunnel_module /usr/lib/apache2/modules/mod_proxy_wstunnel.so" | sudo tee -a /etc/apache2/mods-available/proxy_wstunnel.load
# Enable the module (also make any configuration changes you need)
sudo a2enmod proxy_wstunnel
sudo service apache2 restart