Highland Hardware recently held a jig contest. The winners were announced today and the 1st place winner was apparently the only entrant related to working with hand tools. It is a pretty slick sliding deadman that uses two toggle clamps...one to clamp the free end of the board and the second to force the jig against the underside of the workbench. The jig actually uses the bench's dog holes, only from the bottom side and not the top.
I am still building my bench and had not decided what to do yet as far as a sliding deadman...especially since I am building a Holtzappfel-ish one. This jig appears to be a very viable option for me.
lcombs