Piston soaks are a good method. Ask anyone who owned a Saturn S-Series car for a while. I probably should add something about them to the page I wrote this morning.I'm probably going to give it a shot after I retire, when I won't care if a chunk of carbon falls in a cylinder and scores the walls. For now I'm just going to keep adding oil and change the filter twice a year. If all goes well I will be retiring next year and so I only really need to get another 20k out of this engine if it decides to crater.
I've seen some good video of the PEA working but what I have seen is that you want to do it a cylinder at a time rather than the intake method, let it soak overnight and shop vac the deposits out. I believe mine are bad enough that I can't get a seal tight enough to keep the cylinders clear if I do it like that.
Or maybe not. When done wrong they can do some serious damage (hydrolock). I'll have to think about it.