Thank you for your post.
I suggest you enter this as a product suggestion into our Feature Requests web form at:
These web form submissions are monitored and read by our Development and Product Management departments, where they are then discussed and considered for future releases. Although I could copy your post and paste it into the web form, there are a couple of questions asked that only you can answer.
You can easily do this by setting up a script on any web server that will resolve this for you and then parse the results back into your Filemaker solution.
Let's say you can run PHP on your web server, then add a small php doc (let's call it userip.php):
<?php$uip = $_SERVER['REMOTE_ADDR'];print "$uip";?>Then use the script step Insert from URL with the address to the php doc in the script step options. Use LeftWords to trim away any trailing spaces or carriage returns and you've got your public IP. If you don't have access to a web server then you can use any available website that displays a public IP like http://easyipaddress.com - you will have a bigger cleaning job stripping the results down.