Yeah I'm pretty sure PP would not be a good idea since it's used to rid plants of snail eggs. Not sure it's a very effective ich remedy either. I would just go with upping the temps, maybe 1-2 degrees per hour until you are at 85. Leave it there for about 10 days minimum, I usually do 2 weeks to be sure.
Don't try this if you don't have a way of adding additional circulation and aeration but most of us have some air pumps, powerheads etc. laying around so it shouldn't be hard to do! Also drop your water line so the filter(s) make more splash. The fish will be very hungry and active, but other than that I've never had any issue treating ich simply with heat.
Oh and one more thing, supposedly diatom filters can rid your tank of ich...but I know nothing about this...maybe someone else does?