how to add a few PPV items to already published channel

Hi all
subject says it all - I have an established FREE channel, and want to add a few items that are PPV.
Can't find anything in the SDK about how to have a few items as billable.
Has anyone done this, if so, how did you configure it?

Thanks in advance

Kelly

Here are the scenarios they list:

Free channel to a one-time purchase channel

For example, a user adds a $0.00 channel, has limited access to content and is prompted within channel to buy for $9.99.
One-time purchase channel to a one time purchase channel

For example, a user purchases channel for $2.99, has limited access to content and is prompted within channel to buy for $9.99.
Free channel to monthly or annual subscription channel

For example, a user adds a $0.00 channel, has limited access to content and is prompted within channel to buy for $2.99/month.
One time purchase to a subscription channel

For example, a user purchases channel for $2.99, has limited access to content, prompted within channel to buy for $9.99/month.
Monthly subscription to a monthly subscription, or an annual subscription to an annual subscription

For example, a user purchases channel for $2.99/month, has limited access to content, prompted within channel to buy for $9.99/month. If a customer upgrades from one subscription to another any payments made on the first subscription must be carried over to the new subscription.