You don't want a full pendulum for this, you just want a simple arialised off the ground cast.
Use a longish drop, so the lead hangs about two feet above your top hand if you hold the rod upright (this is just a starting suggestion, you can experiment with the drop later).
Then swing the lead right out behind you, keeping it as close as possible to the surface of the water. To keep the lead close to the water you will have to lower the rod tip as the lead swings further away from you. If you get everything right, when the lead reaches its furthest point from you, the lead, line and rod will be pretty much in a straight line, with the lead still just above the surface of the water.
The trick here is to get the lead as far away behind you as possible, so if you can lean a little and stretch a bit, so much the better. (The further away behind you you can get the lead, the better, because this willmaximise the length of your casting stroke and therefore the power you can feed into the cast.)
Then, turn into the direction of the cast and bring the rod forward in a spear like motion, aiming high and looking high. Once your left arm is straight, or pretty close to it and your right arm about level with your shoulder, you can do the usual pull down with your left arm and push with your right to finish off the cast.
Even waist deep in water, you should be able to hit 100yds+ like this.
To improve distance even more (if you need it), instead of starting the cast by swinging the lead right out behind you, try twisting a bit further and swinging the lead out to about 7 o'clock (if straight ahead is 12 o'clock and directly behind is 6 o'clock). Then, before you start the forward motion you will have to turn towards the direction of cast a bit more and that will give you a bit extra rod compression and therefore a little extra distance.
Hope this helps.
