Weather helm is real common, especially for those of use with maximum rake on the mast.
I've heard of people modifying the rudder, to add rudder forward of the pivot point. I don't believe this is kosher for one-design and you'd probably take a hit in PHRF, but it's supposed to work. I believe this was a forum topic some time ago.
If I may, I'd like to add my $0.02 to something previously mentioned. "Use a smaller headsail". I'd disagree. Weather helm is caused by the center of effort being aft of the center of resistance (the keel). This is caused by an imbalance of force aft of the keel. To correct that, you need more force forward of the keel, or less aft. So to correct weather helm you could reef the main or depower the main, or put up a bigger headsail. My J loves her #1 and is best balanced with it up.
