Here's a pretty easy but pretty scallop edging (I think I remember what the pi shawl looks like--it's the round one, right?).
In some stitch on the edge which will be the beginning of the round, Attach yarn with sl st. Chain 5 (counts as first treble and ch-1). In same stitch, (Treble, ch1) four more times, then end with treble in the same stitch (6 trebles and 5 ch-1 spaces).
Skip about an inch on the edge (whatever interval makes the edging not curly and too full) and (Treble, ch 1) 5 times in that stitch, then treble once (6 trebles, 5 ch-1 spaces).
Repeat this all the way around. When you get back around to the first scallop, sl st in 4th chain of the original chain-5 and you're done. Cut it and weave it in.