SetterGuy, I haven't had the type of scum on our pond that you have on yours, but I have used an outboard motor on a tethered or anchored boat to ease FA to a corner of my pond where I then raked it out. This technique worked very well for FA removal.

I've anchored the boat with two lines out the back. I've also nosed the bow of the small boat into the shore, stabilized the stern with an anchor, and idled the motor for a period of time to work the FA towards a cove on the far side of the pond.

Maybe something like this can help you concentrate your surface scum.