Adding lead at 3 and 9 will be a noticeable increase in swing weight unless you add very little lead. I don't really find it all that unstable on off-center shots. The only time I really notice a significant effect is when the ball actually hits frame.
Try about a half ounce under the butt cap and see if that doesn't make it feel more solid.
i'll give this a try! does the lead HAVE to be under the buttcap? or can i have it on the handle under and overgrip? i'm trying to keep from lifting my leather grip again.