You can't, technically, without special procedures. Devices like this actually define 2%-5% as "0%" for the user in order to protect the battery and ensure it'll get back to charging without issue.
That said, you still want to keep the "full cycle" to once every 60 days or so, because you really are hurting the battery every time it dips below 10-20%. Also, try to exercise a little self-control and leave the iPhone off/alone while it charges back up to 100%.