Wondering if WD-40 and paraffin wax might work?
Scotch Guard?

If you can buy Cavalier brand silicone liquid shoe waterproofer, in a
four ounce bottle with dauber, it's a great fly floatant. I used it
for years, applying it with a small camels-hair brush to the parts of
the fly I wanted to float, but not the parts I wanted to sink (e.g.,
emergers.)

To my great regret I can no longer buy it in these parts, so I've been
experimenting with Thompson Water Seal. I treat the flies when I tie
them, and it's more or less permanent. Now that I have "Cabosil,"
I'll use that for on-the-stream "refreshing."

vince