I changed the whole operation for everyone to public right now. I'll add back an OPTION to make things private later.

The way to handle the exchange is probably to do something like ask for overpayment and then return the change to the newly created account.

The actual mechanics of generating a Lightning invoice via my APIs can be done and then the amount can be more carefully calculated and controlled. I might have to add some kind of way through the API that you can ask for a specific Hive price quote and then get a guarantee that you get the exact amount of Hive when you send the asked for Lightning.