Laziness wins again! (I was going to attempt this.) There's a website, too:
http://waifu2x-avisynth.sunnyone.org/
Translation of usage:
waifu2x(clip, int nr=0, int scale=2, string models=".", int jobs=0)
nr: 0, 1, or 2 for no/light/more noise reduction.
scale: A power of 2. 1 disables scaling (noise reduction only)
models: Location of models, defaults to plugin folder.
jobs: Threads, 0=# of cores in system.