My recommendation would be to attach a small block that can handle a wire line to the clue of your sail.
Buy an outhaul line that is StaSet (or X) that is spliced with 4 ft. of wire. If you have 4 - 6 feet of wire you probably won't need the the "X" type. But the wire will make it more expensive anyway because you have to pay for the splice...
Run the line (wire end) through the boom (from the mast) and over a boom end sheave, into the block which is attached to the slide at the clue of the sail, and terminate the end of the wire (which you had made with an eye) to the end of the boom.
Make sure that your sheave at the end of your boom can handle a wire-line. If not.. All bets are off...
You'll have a 2:1 advantage and not use up precious boom end sheaves.
I have a winch for trimming my outhaul.. but if I can avoid it.. I'd like to. Who wants to fish for a winch handle in the light Chesapeake air. (please don't ask why I have 6:1 mainsheet)
Also. I really hate hardware inside a boom. You can't easily (and therefore won't) maintain any hardware in a boom. (at least I won't!).. It will cause problems before you know it.
Please note I've been traveling for 23 hours straight and am in a small town in Eastern Europe. God knows what the hell I'm doing on Sailnet.... I think I have a problem..