I think you should try some risky trades also. The losing teams in my league seem happy to keep what they have and keep losing. That blows. Try for some buy low guys. I offered one guy Matt Holliday and Kenny Ray for Carl Crawford. He's losing with Carl Crawford, but doesn't want to take a chance that Ray might be closing for Atlanta. Even if it Ray doesn't work out, Holliday is close to Crawford. If Ray does work out, it's a great trade for him. I would look for trades like that. The losing teams need to take risks imo, not the winning teams.
I agree that patience is one of the best strategies, but don't be afraid to make a move that could improve your team. I'm in the same boat as you are with a couple of my teams. I think the best way to improve your team (if it's obvious you're not going to win with the guys you have) is to find someone who is strong where you're weak and vice versa. Make him an offer that will strengthen both of your teams. For instance, I have one team that has great pitching, but not so great hitting (I really need a RF). Another team in my league has awesome hitting, but bad pitching, and he also has exactly what I need (a good RF). So I'm trying to work out a trade were we both benefit. The key is to point out his weakness, and show how much better he'd do with the guy I'm offering. And if you can, trade away a guy that you expect to perform worse in the 2nd half of the season (based on previous years). Maybe the other guy won't notice. Of course, you can also try to trade for guys who are typically slow starters and don't really get going until July. If you find the right manager, you can sometimes get a great 2nd half player cheap.
A combination of patience and aggressive trading is the key.
Since most veteran players generally reach their targeted levels (give or take a little, and barring injury, trade, etc), you are better off keeping Sexson and hoping for a rebound (he has hit .320 with 3 HR and 9 RBI in the past 7 days).
Your idea of trading some of your pitching for some hitting and relying on the WW to improve pitching down the road is a sound strategy, I think. There always seem to be pitchers of some worth on the WW in all but the deepest of leagues. Get some proven bats to bolster your offense, and keep a keen eye out for pitchers showing improvement, getting called up, or facing a favourable schedule.
Target players that aren't performing up to their normal levels. Buy low, with the hopes they turn it around. Play on other owners lack of patience. If they don't turn it around for your team, you aren't really ruining your season, because obviously it wasn't going well anyway. It's worth a shot at the very least. I would even consider trading for players on the DL, such as Colon or Patterson(though it's probably too late to get those two).