not a problem - worked non radar procedural control and used to use it all the time. It had to be requested by the pilot - not initiated by the controller - and you could put any other riders on it as well ie cleared visual approach rwy xx , join via xyz, and even maintain xxxx level until xyz. It just means terrain avoidance becomes the pilot responsibility, and tracking unless told otherwise. With regard to other traffic, some other form of sep is required until visual sep is achieved and then it becomes the pilots respons. for spacing and even wake turb. (helpful suggestions are still a good idea both to help the pilot and avoid nasty surprises- both for them and yourself).
requirement to request is - by day - to be able to navigate visually having the ground or water in sight - no requirement to have runway or even airport in sight.
by night - pilot must have runway lights in sight - not just approach or identifiers - but runway lights.