A Freo supporter on their forum has proposed this:
Richmond 2,19 in for 7,15,26 out ..................... leaves Rich with 2,19,27,28.
GWS 6,7 in for 2,13 out .................................. leaves GWS with 6,7,53,71.
Fremantle 13,15,26 in for 6,19 out ................... leaves Freo with 8,13,15,26,61.