Hi, When I saw your delima....I thought " push rod rom inside" instantly. then I read other replys to your situation and many have the same idea. It is simple....no ropes, no pulleys......a simple little piece of 1/2" flat bar sold in the metal section of at any Lowes or HD. Drill a hole in one end...get a little small L bracked...Mount the L bracket to center of bottom of sash(shutter). Attach the flat bar to L bracket with small bolt and nut, don't overtighten. Pass thru the hardware cloth....hey, if ya gotta snip a wir or to to get the bar thru...so what. Pull window closed with flat bar. Mark flat bar where it meets inside window frame or rough opening. Take file or jig saw with metal blade....make a notch at mark. take the flat bar and cut off about a 4" to 5' piece, drill two holes in in and mount it in the center of opening on the frame with the metal sticking up alittle. Reattach the bar to your angle. Pull shutter closed and drop notch into small piece of metal you mounted to frame....it will keep the shutter closed. hope that makes sense and helps.
Erik