Sure, I e-mailed the general e-mail address I saw on the main page for permission to place the cache in Blue River Parkway, and I got this e-mail address:
StalWil@gw.co.jackson.mo.us
I asked who the land manager was, and he said that it was Jackson County Parks & Rec (so it's not an actual person who is the land manager, but it's the agency itself).
I got several more caches to plant myself, Blue River Parkway Two and Three, and maybe a few along Little Blue River or Landahl Park.