build nginx with full webdav support (nginx-dav-ext-module)

Question

OS: Debian Squeeze
nginx: v.0.7.67

configure arguments: --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-log-path=/var/log/nginx/access.log --http-proxy-temp-path=/var/lib/nginx/proxy --lock-path=/var/lock/nginx.lock --pid-path=/var/run/nginx.pid --with-debug --with-http_dav_module --with-http_flv_module --with-http_geoip_module --with-http_gzip_static_module --with-http_realip_module --with-http_stub_status_module --with-http_ssl_module --with-http_sub_module --with-ipv6 --with-mail --with-mail_ssl_module --add-module=/home/thijs/nginx/nginx-0.7.67/modules/nginx-upstream-fair

And I want to patch this installation with nginx-dav-ext-module for full webdav support. Here's how I tried to do it (with no success so far):

1. get the sources to some folder in my home dir: apt-get source nginx
2. download nginx-dav-ext-module unpack and place it into nginx-0.7.67/modules folder
3. add: --add-module=/full_path_to_source_folder/nginx-0.7.67/modules/nginx-dav-ext-module \ to debian/rules file
4. apt-get build-dep nginx
5. dpkg-buildpackage
6. dpkg -i nginx-dbg_0.7.67-3+squeeze3_amd64.deb
7. and finally start nginx, but nginx -V gives me the same configure arguments as before adding nginx-dav-ext-module (info above)

What am I missing?
Any suggestions appreciated.