I like a Dark 'n' Stormy but I only have white rum at half the alcohol content. I do have lemon-lime cordial, but it tastes more like sugar than lemon/lime.

While you might not have the exact ingredients to make a traditional Dark 'n' Stormy, you can create a delightful alternative with what you have. The Rum Collins might be a great choice here. Though it usually calls for fresh lime juice and sugar, you can substitute the lemon-lime cordial for a sweeter kick, matching well with white rum. The refreshing and light nature of the soda water complements the lemon-lime cordial, making it a fantastic summer drink. Plus, with the lower alcohol content, it will still maintain a balanced flavor without overpowering your palate.

Given your ingredients, you might also consider a Spiced Rum and Sprite recipe substitute. While typically made with spiced rum, your lemon-lime cordial with white rum can still create a refreshing and quick-to-make drink. This combination will blend well and give you a fizzy, citrusy sweet experience, perfect for casual sipping.

Whatever you choose, both options offer a delightful way to make use of what you have on hand while delivering a flavorful and refreshing experience. Cheers!