From the latest version of AwesomeMod:
"addlotsize" <width> [x] <height>: Adds custom lot size to the Edit Town lot plopper, so that sizes other than those normally included can be plopped into your neighborhood, so you can place the missing 60x60, 64x32, 32x32, 16x16, etc. lots you wanted. Lot sizes added in this manner persist until the game is restarted.