I do have some pre-cut ovals and circles that I picked up a few years ago at the Paper Cuts booth at a stamp show. Unfortunately, they just don't nest as well as Nesties, and I have have a limited range of colors (mostly white and cream) as I had to buy them in packs of 25.
During VSN, I played around with these shapes and found I could easily create a scalloped border for them. How? Simply trace the oval or circle onto another piece of cardstock, then take a scallop-edge scissors and carefully cutting out the shape. Cut with short strokes, moving the scissors/paper frequently so the bottom edge of the scallop is always hitting your traced line. The result isn't Nesties-perfect, but it really looks pretty darn good
One tip: trace your circle on the "wrong" side of the paper if are using printed paper or two-sided paper, so you don't have to worry about your pencil lines showing.
Here is a card I created for VSN using this method. I have some other decorative edge scissors, maybe I should experiment.