"Modifying" a basket before payment

We're using CBSubs to regulate access to a library of video seminars. Essentially a user selects a seminar and subscribes to 2 weeks access to the video and associated course materials.

The client seems satisfied with the workflows and processes implemented but has requested that a site user be able to modify their basket before payment. For example: when using a more typical shopping cart (an allegory she falls back on repeatedly, despite our explaining CBSubs simply doesn't operate this way) a user could request an item removed from their cart without losing the other contents of the cart.

The problem she is having with CBSubs is that, were you to purchase access to 2 or more courses but want to remove one from the payment basket before confirming your order and paying, the only option is to click "Cancel Payment" and lose all the contents of the basket.

I'm looking for any information you can provide re: custom development for implementation of this feature, an existing CBSubs plugin to provide this functionality, etc. that might help us to implement this feature for her.

CBSubs is not a shopping cart or digital store. It's a subscription management system. Such a feature is currently not possible. They would need to cancel the basket using the cancel link next to the payment gateway buttons then re-select their plans. We've plans to implement further shopping cart like features with later releases.

CBSubs is encoded so it's not possible for you to edit source and force such a feature. At any rate there's no code in the source to support it so it would likely break CBSubs even if was edited into source.