I've heard that single bills are the norm in the US (I don't actually know if this is true, however), but up here in Canada this is a solved problem.
When you order, you simply tell your server who is paying for what (e.g. "separate bills", "I'm paying for her, those two are separate"). If you don't say anything, they tend to ask before giving you your bill. It's pretty simple.
At chain restaurants in the US, we get a single bill in two inches of space and 10 inches of space with laborious instructions on how to complete their customer satisfaction survey.
When you order, you simply tell your server who is paying for what (e.g. "separate bills", "I'm paying for her, those two are separate"). If you don't say anything, they tend to ask before giving you your bill. It's pretty simple.