I was dying on the GPT-4 API waitlist too. I built a proof-of-concept with GPT-3.5, got some ada embeddings, played around with some common patterns for a couple of weeks, spent less than $20. I then applied to the waitlist again with a few short sentences about what I'd done, how GPT-4 would make it better, and how it would enable something new and valuable for a particular market. Approved that day.

It's not exactly a shortcut, and maybe it was just luck, but I suspect the key is just to start building with what you have and show a trajectory. The best part is that coding with ChatGPT-4 as a "colleague" has made the whole thing super fun.