I would normally advise against QLink style 'Instruction' over the radio, eg- Do this so we can take a 10 knot tailwind and save 30 seconds. However, in some cases it is certainly required. By no fault of their own, some smaller aircraft pilots do not have the proper appreciation of Jet/Turboprop operations let alone a 'commercial operation'. I find often the safer option is to slow it up and let the 172 finish his circuit rather than direct him to remain upwind or extend downwind, but I appreciate this isn't always the easiest thing to do with commercial pressure coupled with the speed of a Jet or Q400.