I've watched him and he does use the overhand method. While he has no problems with full sized pistols, he can't consistently rack the little EC8S back all the way to feed a round.
I would not recommend messing with the springs AT ALL.
Compact semi autos are often a "tighter" balancing act than full size pistols and any changes to the spring set up could invite malfunction.
Have him try this slight change to his method, instead of pulling the slide to the rear, just hold the slide "in place" and
push the grip forward.
For some people this makes enough of a difference.
The slide racker gadget is a neat idea but I wouldn't be paying $25 for a plastic widgit that I could make out of scraps I already have at home. And, you still need a firm surface to push against.
Using the edge of a table, or anything similar is a time proven method, and does work, with differing degrees of ease depending on the amount of "meat" in the face of the slide around the barrel. Some guns, which have square, flat faces on the front of the sights can use the method easily, just hook the sight on the edge and push the grip down. Not the best thing for the finish, but that's a minor concern, isn't it??
I see the Ruger in question doesn't have any flat spot on the sights to use that method, though...
Changing to a different gun might solve his problem, but each different gun can have its own issues.