Showing Product Variant's metafield in Smart Cart

I want to show data that's only available from Product Variant into the Smart Cart. We're using Rebuy's custom template to render the cart in our store. The data I want to process are:

The variant's inventory level and inventory policy.
The variant's metafield.

These variant's data are not available from Shopify's Storefront API and non-product page Liquid template. Using Admin API is certainly out of question as well. Can I fetch these data from Rebuy JS library instead? Considering Rebuy app already has access to our store's product data.