Player never stays on rotating part?

You can easily do this yourself using welds.

--If filtering enabled is on then this should be a script with a Touched event.
--If filtering enabled is disabled then leave this as a localscript

part = Instance.new("Part", workspace)
weld = Instance.new("Weld", part)
local humanoid = Player.Character:WaitForChild("Humanoid")

  if (humanoid.RigType == Enum.HumanoidRigType.R15) then
        weld.Part0 = Player.Character["LeftFoot"]
        weld.Part1 = part
      elseif (humanoid.RigType == Enum.HumanoidRigType.R6) then
            weld.Part0 = Player.Character["Left Leg"]
        weld.Part1 = part
      end

Let me know if this works well. I'm pretty interested and I haven't actually tested yet.