Mike came up with the following: Dohnanyi's sly and wonderful Variations on a Nursery Rhyme plus Kodaly's Dances for Galanta or Liszt's Mephisto Waltz. I suggested swapping out the Liszt or Kodaly for a couple of Brahms Hungarian Dances. The Concerto might also work well with Petroushka or another Stravinsky orchestral work. Or some Debussy, though I am stumped as to exactly what. Or...how about the Janacek Sinfonietta?
I wonder, though, if the best companion to Bartok isn't more Bartok. If you were a little insane, you could start with the Concerto and put all three of the piano concertos on the second half; they fit neatly on one CD, so why not? Go ahead and hire more than one pianist, since even the Third is not exactly easy. Or conclude with