I was just showed a pretty cool trick. Tie your spinner rig as normal, but between the last bead and the first hook, take a piece of spinner wire, make a loop in one end and run it over your leader. then tie on your hook. thread the prawn onto the wire. it will hold it straight and then hook your hooks to the prawn.
If that does not make any sense, I will rig one and photo it. Probably with a Salmo attached to the hook, but you'll get the picture...