I did this just yesterday…The following worked for me. Hope this is what you are wanting to do.
1. On the layer that holds your mask, Hit M for mask, twirl it down and select the “Mask Shape” parameter. Crtl+C on Win, or Cmd+C on Mac. This copies the mask vertices…you should see them all selected in the comp window.
2. Go to the layer that has the Particular plugin assigned and twirl down the effect into the “Emitter” and select the “Position XY” parameter. Ctrl+V on Win, or Cmd+V on Mac. This will paste the vertices’ positions as keyframes. All of the keyframes between the first and last will show as “roving” keyframes…if you want to change any one of them just right click it and turn off “Rove Across Time”