If you want a URL that does not change every time you create a new tunnel, you just need to upgrade to Pinggy Pro..
Once you sign in, you will be presented a dashboard where you will find your access token.
You will also find your persistent subdomain in the dashboard.
Command to start a tunnel to port
8000 and with token
ssh -p 443 -R0:localhost:8000 firstname.lastname@example.org
8000 with the port where your service is running.
b0b87d56-653f-45fb-98d9-8e43779c9081 with your own token from the dashboard.