Only way to do this is probably use a CB Query Field to query the database to see if their subscription is auto renewing or not. Next you'd add a conditional to your mailer for this query field so it'll ignore users that have auto renewing. However, this will require a Professional subscription. There is no feature or parameter for the mailer to check if the subscription is auto renewing.

Really! That's quite surprising... one would naturally assume that the business analyst would have anticipated this need and had support for it built in to the basic "reminders" module.

We've plans to add more and more features with every release. I'm sorry, but we just can't cover every use case instantly. We're doing the best we can to provide all the features everyone needs. In addition to this feature we'd like to be able to condition based off gateway used, payment type used, etc.. we've many plans to improve the mailer and other usages.

What else do I need to purchase (aside from "Professional" support subscription) - in order to implement this much needed functionality??

Nothing, just the professional subscription for CB Query Field. I can't guarantee it'll fit your needs though. You'd need to write a query to query the database for their active subscriptions renewal status to see if it's auto renewing. This can get complicated if you have multiple plans.