
As you know, a degree of convergence at the trot is acceptable (long discussions at AGMs about it!), but not so much as to be single-tracking. Personally I would try road
walking (not trotting and
not pacing) for a while, but also running. Trotting is the action which accentuates single-tracking so you want to build up the other muscles to counteract that.
But that's what logic tells me, rather than actual experience, and I could be talking a load of hot air! :(