I used my lunging system (the one from sstack.com) and Vega did great! When there was pressure on the bit she'd move her head up, and then when she brought it down, she'd have relief. And after a few attempts of lifting her head, she kept it low
I did this at the walk and trot, but only for a few minutes.
I think that will help Blu with accepting the bit and also engaging his hindquarters as well, and I think in turn, helping him with become balanced (which may be a reason why he'll trot and lope without control) and hopefully help with turning.
Honestly, I am very happy I purchased it. I have an extra one if you're interested in it