I've found that stretching the tip of my rod a ways upstream right at the end of the cast can help considerably, and make for less mending. It's not a pretty technique and wouldn't be good for casting dries, but wet flies don't have to be pretty.
I also like to keep my rod tip up real high and keep a decent tension on the line during the drift to keep as much of the line up out of the water as possible. Don't be lazy about stripping in excess line during the drift, and you can start letting it back out on the downward swing. This reduces drag and makes mending easier since less line has to come up off the water.