I was lucky because one of my very first instructors emphasized the importance of footwork and drilled the shit out of me. I remember spending way too much damn time shuffling around in front of a mirror. There's a drill where you square off with another fighter, and place your Kali sticks in a diamond between the two of you and use those to move opposite eachother. Spend a lot of time dancing in front of a mirror watching your feet. Make sure you are NEVER in a position of imbalance or lower body vulnerability. You should be able to cruise around front/back/sides/diag in a left and right lead and always keep a proper foot distance. I use to train on a slippery surface such as ice or linoleum sprayed with silicon to develop a good moving foundation. I also used to place different types of gound around a heavy bag or in a general area where I trained myself and others. While dancing around a bag, you would find your feet sticking to to rubber for one second, slipping on a smooth surface the next, sliding in gravel, then sloshing in mud. It was interesting and required constant subconcious attention to your footing.
my feet are basically big iron blocks
I love to see an opponent stand still or not move his feet much, its much easier to evaluate him, and therefore typically beat him. Force yourself to keep moving man. You know the deal about being stationary or setting patterns. Not good. Telegraphing non-action is just as bad as telegraphing an action.
Just tell your instructor that you're uncomfortable with your footwork and you'd like to focus on it for a while. If he doesn't recognize the significance of this, find another instructor. A seasoned fighter will take advantage of poor footwork easily despite even a high level of upper body skill. Your instructor should be making you mix in Sipas and such while you are drilling Guntaks(or whatever those damn things are called) simply to be aware of your lower body and recognize all dimensions of fighting.
Anyway, I think simply evaluating yourself in the mirror while shuffling all over is a good start. Record yourself sparring and see where you tend to plant yourself too much or fail to keep your feet well positioned and make a concious adjustment in the following training sessions.
You can tighten up the double end bag to change the range(and speed) of rebounding movement. Go everywhere you can, 360 degrees.