Because power cleans are not a max attempt clean, it should be a weight you can quickly lower down. Since I consistently do oly lifting, I have the flexibility. To bring the bar down without dropping it. If you too have the flexibility....this is what u do...
You put the bar on your thighs real fast....as soon as it touches your thighs you squat down, sit down and put th bar down with control. It will hit the floor a bit.
Doing this shouldn't really hurt your shoulders if your shoulders are healthy. Another method is to do power cleans off pins in a power rack. Sit the pins below knee or at the knee. You can, with control lower to thigh and quickly put it back on pins. After many reps it starts to feel lighter.
Linear progression method is probably the best. If you have fractional plates, it would help more than any program you may choose.