Pre-filling shopping carts in Magento

Hi guys! I’m trying to build an agreggation site which summarises products from other Magento webshops and when clicked, deep-links and skips the checkout in the actual shop to the ‘Payment’ page. What are the ways to achieve this, such that size, colour, etc can all be passed over from initial aggregation page? I know does something like this but without the pre-filling of size, colour ,etc.

Any examples of sites that already does this, or plugins that can help with this?

submitted by /u/gmkung
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