I have done exactly as you have described- properly spaced four holes to accept "feet" of my Kapex. All I did was use two thin strips of oak, perhaps 3/8" thick, each with two holes. These two strips run front to back and when I place my Kapex in position there is absolutely no need to clamp or other wise secure the saw. I use the Ron Paulk Ultimate Miter Box stand, modified to fit my needs. While in my shop this platform sits on top of a roll around cabinet which houses a variety of other tools. Since this set-up is on casters I can easily move it anywhere in my shop as dictated by the size and length of stock. When I go out on the job I simply set the UMBS on a set of saw horses. In either situation my Kapex simply sits in the correct position without any clamps. I have many hours using this set-up and have never experienced any difficulties with the saw moving unexpectedly.
Hope this isn helpful.
John