Well, 24 hours and 0 replies since my OP, it would appear that if anyone is using the CN app to pay their Boost Mobile bills, they must be on a different forum.
If we ever decide to give the app a try on Boost, I will report back on how successful it is / was. Thanks very much anyway and may you all have great success with your CN payments!
I don't have a Boost plan..... but would guess it to be relatively straightforward, as it is with Sprint. Perhaps send a message to CN Support and see if any info is needed in the optional field.
One final update: I went ahead and tried a Boost payment. With a little help from the CN support agent (I forgot you need to put your cell phone number, not the account number), the payment went through in about 24 hours. The CN app reflected the payment, and the Boost Mobile account page shows the account credit. Success!
You're most welcome! Here's one more tip that you probably already know, but just in case: Use your cell phone number that is on Boost for the "Account number" entry (the first line under "Payment Details"), not your actual account number.
Enjoy your new phone and good luck with your Boost payments!
Thanks, Diedrich_Duo for reporting on the Boost payment. As far as I can find, this is the first reported payment to Boost via CellNuvo. Nice to know it works as intended!