Hi all,
I wanted to let you know that I created an add-on that allows you to create a form that has a drop-down menu or radio buttons to switch between a single product or a subscription: Gravity Forms Subscriptions Add-on.
I was having the same issue as this support topic, and I wanted users to be able to choose one-time payment or recurring payments instead of setting up two completely separate forms.
It's in version 1.0 right now, so please let me know if you encounter any issues. Also, let me know what you think on the plugin support forum!