You will need:
A whip cream or any aerosal can(must be completely empty)
A can opener
Magnets (rare earth or ceramic)
and a hot glue gun
Step 1: Step Uno
Right along the bottom of the can the should be a metal lip like thingy for the base. Right above that put your opener on it and start cutting. You will have t cut a small dash to let all of the spray that is left out and then continue till you have the base completely off the can itself.
Cut the hose with some scissors or a knife to make room. Yes the spray tip will not work anymore.
Clean it because it will most likely have some residue left in it.
Step 2: Gettin Yer Magnets
and glue them slightly above the inside end of the can.
if the can sits higher on one magnet then the other heat the side of the can until the glue melts slightly and slides the magnet into a position that fits.
Step 3: Its Almost Spy Like....
You might need to do a little bending around where you cut to make it fit but this should be ready.