Sorry, but I can't see how trotting him over poles will teach him how to pick his feet up?
Horses don't instinctively know how to balance themselves - we have to teach them. So it's up to you to put his feet in a position, before you try and pick them up, that he's not going to loose his balance and fall over.
Just keep backing him up or moving him forwards, a step at a time, until his feet are in the right position. If you're trying to pick up a front foot, his back feet need to be roughly even, and on the front ones, the one you're trying to pick up should be slightly further back than the other one. Same with the backs - if you're trying to pick up a back foot, the front ones should be even and the back one you're trying to pick up should be slightly further back than the other.
If he's standing four square on all four feet, he won't be able to balance, and if they foot you're trying to pick up is ahead of the others he won't either. Then pick up the foot for just a second - a brief pause off the ground then back down again, and slowly increase over time.
He will eventually learn to balance himself and put his feet in the right place as soon as you ask him to lift it.