RSS feeds to Email, on the fly

I have a web app that generates RSS feeds. I would like to offer users the ability to subscribe to these RSS feeds by email.

I know I can use Feedburner to manually burn my feeds and offer email subscriptions. The problem is I offer hundreds of RSS feeds and don’t want to manually burn a feed just for this one feature.

Does anyone know of a service or API (preferably free) that allows you to create an RSS feed to email sign up on the fly? Any help is much appreciated. Thanks.

-Ace