I don't know whether you can drop the feed dogs on that model (although I can on my old Kenmore, which is about 3 years older that yours). You may be able to adjust the pressure regulator enough to do FMQ. Here's a link for the manual for the 158.12512, which is essentially the same as your machine.
http://www.managemylife.com/mmh/lis_...M/1009324L.pdf