We did the same thing at canter. I counter flexed him in the canter until he softened. I also did some changes of lead through trot which didn't start out too well. Speedy was really ignoring my outside rein, so I worked on some pretty strong half halts.
I am doing this work in a short court, so once or twice I circled at A to rebalance him and myself. Once he felt pulled back to together, I made the ten-meter half circle, which was more like 12-meters, pushed him back to the rail, and then did the 20-meter half circle in counter canter.
I think we'll do the change of lead through trot on the long side next time. I think Speedy's a little more capable than I give him credit for!