I agree with Don... a handle with a front frame piece works well. We not only keep guiding the trainee in smooth control inputs, but also in turning with the model. If the newbie gets dizzy or confused, either the handle is let go or it is arm wrestled over. Either case, the trainer can -or should- overrule the incorrect moves.
It also allows a little 'dry-flying' with the student. Example: before a first flight, trainer stands somewhat to the right, behind trainee, left hand on trainee's left shoulder. Trainee is told to walk backwards in a small circle as the trainer walks forward the same way. Again, the trainer controls or influences) the learner's moves. (Adjust 'handedness' according to the individuals involved...) A handle should be shared between them as it will be during that first flight.
Trainer holds handle around the front frame piece so the learner has the actual grip. After 'initiating' the learner in stepping safely and correctly, have the learner 'ride along' for several laps without applying inputs, then allow gentle inputs as directed by instructor. When it appears the lesson has been mastered, the trainer should continue circling with 'his' hand on the front frame or just in front of it so as to intervene if necessary for any unwanted inputs or stumbles or panic.
After several laps of riding along lightly, and if it feels safe and appropriate, the instructor can come off the handle, step back - but not too far - and guide the trainee verbally. After conditioning the gradual and small control corrections that work, it should be safe to let the trainee land the plane with verbal guidance and encouragement when the time comes. A little explanation before the 'silence' should prepare the guy for his first successful landing.
It is a bit awkward for the instructor, but a little practice switching hands while flying solo will overcome that. Need I add that for this business, thongs are not only irrelevant, but dangerous? After a successful solo, stress thongs for every flight, of course (you may add a wink-wink-nudge if you must...)
And anyway, don't most good handles have either a single front piece or a partial piece above and below?