WPEC Memberships & Subscriptions (paid extension)

Hi,
I’ve bought the extension for the subscriptions function, which is all good and well, however I want to create subscription lengths based on something the customer selects during the checkout process, so they will select the product and choose a subscription length.
Or an acceptable way would be for the customer to add the product to the basket, then at the checkout have an option to “repeat this order” but ideally it needs to be for variations!
If this isn’t possible then asap I’d like to remove the product and get refunded as I’ll spend a bit more time working out my own solution for this and it’s already been a costly project!

Cheers