I haven't tied or fished a crease fly yet so I may be off base but here goes.
Since the flies are for pike why not make the foam sacrificial, and bring extra bodies to glue on?
Skip Morris has a book about tying flies with foam. In it he had suggestions on how to preserve the color added to flies using permanent markers. I only looked at the book in a book store but I think he coated the flies with a diluted shoe goo or soft-tex.
I've used fabric paints on foam body flies before. They have lasted well, but, they are on a solidly supported surface rather than a crease fly where the foam can flex.
Whatever you do Pete I know from seeing your flies in the past that they will look good.