My range officers and I have made one handed shooting and reloading a requirement during firearms training.
With the penchant that suspects have towards shooting at the threat (Gun) this seemed like a necessity. We found that during simunitions training that our role players(instructors) were constantly getting shot in the hands.
Starting with Platt and Maddox in Miami and the FBI agents being struck in their hands and arms rendering them practically useless.
The technique we teach is the holster placement then reloading with the available hand. However, to charge the round we have them charge off of their duty belts, using the rear sights and pushing off, down and away from the body aggressively.
We also inform them that they can charge the weapon by dragging/pushing the rear sights on the cruiser door, pavement, edges of counters, etc.
The reason we don’t teach going to a knee or using the heel of the boot is because it limits the officers mobility. They are already under duress and by allowing them to move while reloading it may allow the officer to move to cover while readying the weapon for a potential re-engagement.