You could script something like this on the host computer (this is for a Mac; I'm sure there is something just as simple for Windows). Then put it into an automator app. This doesn't require anything from OpenLP. It's safer, especially on a guest network to use the default port, 4316.
If your host is hardwired, use en0 in place of en1 in a script like this:
echo "http://$(ipconfig getifaddr en0):4316/" | /usr/local/bin/qrencode -o - | open -a Preview.app -f
This requires you to install qrencode software once, say, using brew install qrencode
The equivalent action in Windows would go in a batch file.