Balance your Imperial. All you need is some "sticky tack" -that silly-putty like stuff that's for sticking posters to your wall. This process might be posted somewhere else, but this is what the great Jon Gates taught me years ago:
First, the cap can go on two different ways. Spin the top with the cap on each way, and determine which is smoother. MARK IT. I scratch mine with an exacto knife so I never loose the mark - a line connecting the cap and the bottom. Take a blob of putty (sticky tack) bigger than a BB and smaller than a pea, and stick it underneath the cap near-ish to the rim. Spin it. If it's worse, move the putty to the opposite side, step and repeat until you get the best result. Next try it with a little more or a little less putty in that same spot until you get the best result. You'd be surprised how much difference it makes. It takes some time but it's worth it.
As far as a mod to make it heavier, I'm sure somebody in this forum has come up with a descent mod, but I've always wanted to tape it up, dump a bunch of silicone in the hole in the top and spin it in a drill or something until it dries. I have a trouble waiting for things to dry, so I've never tried it.
-Chris Neff