I've topped mine of two different ways, and didn't remove the radiator covers with either one.
Find the overflow hose hanging below your bike. You can fill a squeeze bottle and fit it in or over the hose and force it into the reservoir. Put a pan under it to catch the fluid that will run back out of the hose.
You can actually reach around behind the radiator cover and remove the rubber stopper with your fingers if you're careful. Use a baster or squeeze bottle with a hose and put it in from there, then replace the stopper. It takes some maneuvering with your fingers to get the stopper back in.
And last, if the coolant is on the low level when cold you're still OK. It will rise to the upper level when it warms up.