Ross spring switches

Piano wire is the right idea. Upside down U with one end in the throw bar and the other end glued into a hole in the table top is probably what I would do. 

I use .025 music wire from K&S. Works great for non derail as well as much less lmpact on the switch rails. Takes a little tweaking to get it perfect. 

Tom, is the idea that a train enters from the right, takes the lower route through the switch, then goes around the loop to come out on the upper leg to temporarily push the points down as it moves back through and then they return to the original position for the next run through? I take it this is when you want trains to use the same route all the time?

Yes.