Ok I got it to where it works every time. This could have been the way I did it before years ago but I don't remember. You have to hit RESTORE for 4 seconds or so then after you let it up you have to press the power switch up to reset the system. then it will reset into the other KERNAL. In your case JiffyDOS. If you want to go back to the original KERNAL you can power cycle or repeat hitting RESTORE for 4 seconds then reset button.
So RESTORE does switch the KERNAL but you have to reset the system for it to boot into it.
EDIT: Oh I see this is the way you already quoted that doesn't work. Hmm. Maybe try a different EPROM? I can send you the one I made if you want? It is an SST 27SF256 flash ROM. You can erase it and reprogram it anytime you want.