One possible option, depending on your dinner habits, would be to ask for the bill right when you place your order - especially since your friend would likely be getting their bill at the end of the meal as usual, it makes it a lot less likely for your bills to be mis-divided, and since the bill is generated so close to your order, it seems like it would be less likely to have any errors from mis-remembering who ordered what.
We started to ask for the bill upfront like this when we were in a rush (have someplace to be, or a long drive, or it's getting late), but once we realized it was a possibility we have started to do so more often just because it's convenient - and even "avoiding confusion when splitting the bill", or "so I don't have to worry about it later" are perfectly reasonable explanations (or indeed "someone mentioned this neat trick") if you feel you must say why you would like it so early. Just make sure you communicate clearly that you only want your own bill to the server, and that it doesn't mean you have to cut out early to your friend (unless you want to, of course) and all should be well.
This trick works really well for us because we rarely get additional chargeable items - usually no dessert, extra dishes, or chargeable drink refills, and if we do it's not much bother to order up front or pay separately when it happens so rarely. Obviously, if you habitually get these add-ons, then you would ask for the bill later in your meal than if you do not. Alternatively, a person can use this trick to avoid ordering those kinds of extras if they would like to consciously cut back on them.