I have am working for a website that sells subscriptions to virtual products. They are running on WooCommerce, and they are requesting what seems quite a complex feature to implement.

The website uses:

WooThemes Subscriptions plugin

WooCommerce BrainTree checkout plugin

I need to enable very customized subscription signup's from an external page, without changing their current checkout page.

Now i see 2 possible options:

1) Create a new checkout page on some slug like /Payments, auto add
the desired product to cart, and only display the checkout form.
This entire thing would then be iFramed.

2) Use the WC api to, create an order, pay for the order (Payment
details would need to be sendt via the API?), create an account for
managing that subscription
(the account creation also needs to be automated and take place after the order has been paid for, atm it seems that 
WooCommerce creates the account prior to fulfilling the order).

Does anyone have any experience doing this that can recommend an option?

Best Regards