Ideally, of course, the accordian player could shut up, and the fiddle could play softer, or not at all. I either use the mute, or the whistle and I take turns on the breaks. Muting an accordian is not real possible, and, with most of the accordian players I know (note: I said most getting them to stay out once in a while is not an option either. (Bill Sables is NOT like that, OK?)

Tunes with a high part:
Angeline the Baker
Rakes of Mallow
Gal (Girl) I left Behind
Kerry Polka
Old Joe Clark
Cluck Old Hen
Over the Waterfall
Swallowtail Jig
(doesn't exactly have a High part, but it will overblow well)
That's a start, anyway.