I wouldn't cleat the mainsheet.  She's a little boat, probably weighs less than you, and things happen quickly.

My solutions to getting a free hand long enough to scratch my nose are:

- A shock cord "tiller tamer" to be able to let go of the tiller for a few seconds without it getting away from me.  I happened to have a 42" one with soft plastic hooks large enough to stretch from rail to rail over the gunnels at the aft bulkhead with enough tension to hold the tiller if I grab a turn and slip that over the end of the tiller.

- A ratchet block worked into my sheet tackle.  I've used a midship two part sheet on my lug rigged PMD.  If I'm by myself, I rig that ratchet block to the mast just below the lower yard and run the fall of the sheet forward through that and then back to my hand.  If I have crew/passenger sitting forward, I'll substitute that ratchet block for the upper block in the two part tackle, with the fall exiting the lower (non ratchet) block to my hand as usual.  Either way, the sheet still eases when released, but takes very little effort to hold.  This means you can hold it in your teeth (I'll have to quit sailing if I ever lose my teeth--I don't reckon Polygrip is up to the task!) or by pressing the fall between your knee and the thwart or maybe against the bottom under your toe.  I've also had some success passing the fall over my knees and holding it with my tiller hand.

- With the midship sheet arrangement, you can also sometimes get away with pulling a slipped half-hitch around the two parts just above the lower block, keeping the fall handy to release the slip knot in a hurry if needed.  There is some risk of a jam precipitating a hard chance if a sudden gust has over snugged your slip knot, and I've quit doing that in favor of the ratchet business described above.

The two capsizes I've had so far were the result of failure to move my weight quickly enough during a tack or gybe,   I can put the rail down far enough to tip her simply by leaning over the side a bit--doesn't take much.

Your milage may vary....

.....Michael

+1 on the ratchet blocks. I've got one on my Faering Cruiser and had 2 on my schooner.  Don't forget the stopper knots.

Laszlo

Over the years I have owned (and raced) a wide variety of small crew balasted boats and have always had a cleat for the main.  The trick is to recognize when you can use it and when you should not.  If the wind is blowing hard enough to capsize you, you probably should not use it. 

   I never cleat the mainsheet on my lug-rigged dory. Instead, I just wrap the mainsheet once or twice around the end of the tiller extension. That way, I can hold the mainsheet and the tiller with just one hand. The other is free for scratching my butt or taking a drink.

Give it a try.