Here are a couple of pictures. The boat is in a bit of shambles now, recovering from the trip, but I'll try to make it clear.
The mizzen sheet leads aft from the cam/swivel in the foreground of the first picture to a large single block in the back, just in front of the transom. That block is held upright by a spring. The cam/swivel is, if I recall correctly, from Ronstan. The single block in the back is from Garhauer. The sheet comes out of the cam/swivel at a convenient location where I can set it from the usual helm seat just aft of the main thwart.
Then the sheet goes up to another single Garhauer block, also on a spring, mounted on the top rail of the transom, then up to a single block with a snap hook that attaches to the sprit. In this photo, the snap hook is just latched onto one of the mast halyards, for illustration only, since the masts were lying on the boat and the sprit was elsewhere. Normally that block with the snap hook would be a few feet up in the air, along with the end of the sprit, instead of drooping down as it is in this picture. As you can see, the snap hook is on a little dynema tail I made, simply because the snap hook itself wouldn't fit into the sheet block shackle.
From there, the sheet goes back down through a mirror-image set of blocks on the port side so that I have double-ended sheeting.
I've seen other systems, include one that Alan uses on his 17 that is probably a bit simpler. This works for me. I like having the heavier braid for the sheets, just to have something to hold on to, and I like having the cleat close to where I sit. I usually sail with the mizzen cleated and hold the main sheet in my hand, uncleated, ready for quick dumping if needed, especially beating into the wind.
Let me know if you have any questions!