Go with a webbing to hold the clew down. This does not need to be tight, any sail maker who knows their stuff can knock one up, most are a valcro sewn to the webbing and this passes around the boom and through the eye a couple of times, and do away with the slug.
Heaps of production boats go down this line, most because it's way cheaper than a track and car setup, and performs in the same manner for 90% of users.
Check these links out:
http://www.hydesails.co.uk/accessories/clew-strap
http://s213.photobucket.com/user/Fas...rap-1.jpg.html
Quick and easy solution..
Cheers