A tiller extension is a must on the dinghy. You can hold it between your knees while adjusting other lines. I do this all of the time on my 5o5.
A line running between two aft cleats, one on each side of the boat, with a clove hitch going around the tiller works really well. I liked it better than the tiller tamer, which always felt like it was getting in the way and added friction to regular steering.
I have used the Davis, and it's alright. I'm currently using the Wave Front Tiller Clutch (as mentioned by a previous poster) on my Precision 23. The tiller clutch is vastly superior to the Davis. It sets instantly and releases instantly. Very easy. It's really one of those devices that's so good, you wonder how you got along without it.
I've unfortunately not seen it available here in the UK (or should I say luckily, otherwise I would have another job to do on my wish list): I quite like the idea of the Forespar extendable tiller extension that can be locked in the cockpit coaming with its proprietary tiller lock.
An icicle hitch tied to the tiller, then looped around a deck cleat makes it easy to control the rudder from anywhere on the boat. I've actually gone below and made a sandwich all the while staying in course by just pulling and giving in the line.
Just tried the "Cajun tiller tamer" today. Light to moderate winds just around 10 kts. Also worked for holding course while using the outboard allowing you to put things in order on returning to marina. Simply a line, 3/8, tied from stern cleat to tiller with three turns around tiller from beneath, the tied other end off on the other stern cleat. You tube has a video that shows it very well. I'm impressed. Ultimate in simplicity and when you want to let it off, simply slide the coil to the rear of the tiller. Worth a try. Can't beat the cost!
I just use a line tied off to each side with adjustable slip knots.
Specifically I have an alpine butterfly to loop around the tiller (this is a type of loop in the middle of a line) and an adjustable grip hitch tied through U bolts on each side which I can slide up and down to adjust tension.
Using this line is typically my preferred upwind sailing strategy and when properly adjusted it sails the boat better than I can can.
I'd suggest rigging up some kind of line and seeing how you like it. You may find a new piece of equipment unnecessary.
I prefer the TillerClutch because of the very fast, simply-made adjustments that can be done with one hand. I tried the home-made rigs. They worked fine in light air when I had the leisure to futz with it until it was just right and I wanted the boat to sail while I ate a sandwich and a beer while sitting close to the tiller. But they failed me when things were more critical and I needed to make small adjustments in a dynamic situation (choppy, gusty, sail set adjusments, etc.).
"Also worked for holding course while using the outboard allowing you to put things in order on returning to marina." This works for me using the rudder tiller and locking the outboard steering to straight-ahead, but it reduces the effectiveness of the rudder. I've read some descriptions of connecting the motor to the rudder/tiller so that the two will move in tandem. I might try doing that to my boat someday when I have more time to rig it up. In other words: highly unlikely.