Heinzer: very interesting setup, but I'm not sure I'm interpreting the photo correctly. Is it an eye spliced into the middle of a the sheet, and then passed through the grommet?
Yes, the eye is formed with a Brummel splice.
Also, how is the... purple thing constructed? Is it stiffened in any way?
The purple toggle is a piece of old 3/8" double-braid sheet doubled over. I stiffened it slightly by using hot-melt glue to hold the two sides together and then put a whipping over the whole thing. I could simply have used a larger diameter stiffer line but this is what I had.
I'm surprised to hear that it doesn't hang up on an inner stay, especially the protruding part.
It probably would. I use this on the staysail (set on the inner stay) on my cutter rig. This sail does not overlap the shrouds so there is nothing to get hung up on.
I use a similar attachment for my asymmetrical spinnaker and my drifter sheets. This lets me use the same sheets for either sail. I keep the sheets rigged on deck even when not using either large sail.
I tack/jibe the drifter/spinnaker through the slot between the inner and outer forestays just like a genoa. These sheets do occasionally hang up on the inner forestay but a quick tug releases them.
I use the lanyard "luggage tag" hitch on my jib, flown on the outer forestay. It has never hung up on the inner forestay itself but would frequently get caught on one of the piston hanks of the (inner) staysail. I solved this by replacing the offending hank with a smooth carabiner.