I'm the creator of ngrok.
You can still make this work with ngrok, you'll just need to decide on a few subdomains up front that you want to use for testing. ngrok lets you forward multiple tunnels via the configuration file (https://ngrok.com/usage#config) Example configuration file:
tunnels:
one.mysite:
proto:
http: 80
two.mysite:
proto:
http: 80
three.mysite:
proto:
http: 80
This will forward
one.mysite.ngrok.com -> 127.0.0.1:80
two.mysite.ngrok.com -> 127.0.0.1:80
three.mysite.ngrok.com -> 127.0.0.1:80
It's not a wildcard (ngrok doesn't support wildcards at the moment), but having a few subdomains setup should be good enough for testing, I imagine.