yeah,
Magnatising is a peice of cake.
Little bit of GreenStuff and SuperGlue in the arm socket holds the body magnet perfectly. then you just have to cut the ball joint on the arm in half and GreenStuff SuperGlue the arm magnet on.
extra GrotZookas?
The original GrotZooka! this dude made the GrotZooka design years ago! 
Although these cost $20 for 3
If you want to convert your own check these out, I think they are great
GrotZooka Convertions Created by
CommissarKhaine (from off of DAkka!) these are made using the Big Shoota and Scorcha bits from the KillaKan box.
Panic...