Here is an example of how you would manually install and build a plugin on your server:
I installed this plugin on asia.wiki.org by cloning it from its repo and building it in place. I used the https access rather than the usual ssh since I don't keep credentials on this server. github 
ssh root@asia.wiki.org cd /usr/local/lib/node_modules/wiki/node_modules git clone https://github.com/WardCunningham/wiki-plugin-plugins.git cd wiki-plugin-plugins npm install grunt build
I didn't have the grunt command on this site so I had to install it to continue. npm
npm install -g grunt-cli