You could spin up a VM that has a browser in it and use that to create the account and destroy the VM afterwards. You could use selenium with headless chrome.
If you have a smart phone running any browser there, you could use that.
There are some auth checks to make sure that a single person isn't signing up multiple accounts to get the free credits and if that sort of thing is a deterrent to you using it you may find it difficult to use.
Well, I'll wait for those anonymous/public rate limited keys or a noscript/basic (x)html registering process, or www sites which will propose basic (x)html form based prompts.
Actually, best-effort, temporary, public keys would be more appropriate for their web API waiting for them to do a proper job at working with noscript/basic (x)html browsers.
The raw curl (or python, or node.js - or other those are just the samples) are browserless.