How can I automatically adjust currency at checkout based on customer location?

[LoveAnarchy]

I am currently using a permalink to drive traffic directly to checkout with a pre-loaded cart and discount. I am looking to make it so that the currency will be automatically adjusted to the customers location. I have multiple currencies setup through Shopify payments and if an alternate currency is selected on the storefront beforehand, then the correct currency shows at checkout. However, with the method I'm currently using, skipping straight to checkout, there is no opportunity to change the currency. The permalink therefore will always load the default currency (GBP), assuming the customer hasn't already been on the store to change currency. 

I would be grateful for any possible solutions, as I think a localised checkout link would be very effective for conversions.

Thanks!