Open up the window/animation editors/graph editor window, select the curve, and then at the top you should see a drop down box labeled tangents and select linear. This will move the link a fixed amount for each step so they will not bunch up at the start and end of the animation.

By default the tangents are set to "flat" which has the same effect as "ease in" and "ease out" in older versions of Maya.

Then you just need to tinker with the number of steps when you do the attach to motion path to get the link moving the correct amount for each step. It's tedious but I have not seen a script or plugin that is general and makes this any easier.