"Old age smartass attitude on."
I used the Zone system as proposed by AA for over twenty years. I have to admit that I got some pretty decent prints using it. However, I have found that my exposures and the resulting prints are much better since I have gotten away from all of the spot metering, previsualization and accompanying mental gyrations, and gone to incident metering. Do I previsualize the zones any longer? Nope. Do I worry about whether I will have a perfect Zone II, III or IV for shadows? Nope. Do I have the tonal values that I want on my prints without all of the thinking? Yes, I sure do. Of course at my age, please understand, that I have a somewhat smaller supply of brain cells left then originally supplied and I damned sure don't want to wear them out by using them unduly.
Incident metering (using BTZS principles) does in fact work better in my experience then the Zone System. While the Zone System, as promulgated, is based on reflective light readings, there are other ways to get better results then the Zone System (again in my experience).
Now back to the original question that the originator posed...is it possible to practice the Zone System without a spot meter and additional backs? The Zone System as it is written?...NO (This will change my original response)
Can equal or better results be obtained without the spot metering, additional backs, and mental gyrations? Yes
"Old age smartass attitude off."
As you've already figured out, Ara, trying to do full-blown Zone System work with roll film is tough. With the Hassy, you either need to spread your exposures between (appropriately-marked) magazines, or opt for an alternative approach that isn't quite the Zone System (but might be just as effective in producing good images). I would also point out that a total of 3 magazines only covers N, N-1 and N+1. If you encounter an N-2 situation, you're stuck. ;)
I would agree with the observations of others - if you're going to meter small areas of a scene, a spot meter is convenient, if not essential. At a distance, even a 1° spot can be wider than needed to isolate individual tonal areas.
Personally, I use a combination of incident readings and spot readings with a Sekonic L-508. The incident reading tells me what the exposure would be to render everything at its "true tonality", and the spot readings tell me where individual areas would fall in relation to the film's ability to capture the luminence range of the scene. Once armed with that information, I can decide how I want to approach the exposure, and whether I want to try to compensate with a variation in the development. That decision is much easier with sheet film, of course.
If faced with your situation, I'm not sure that trying to implement the Zone System is really practical. I think I'd suggest just continuing to use incident readings, and taking more pictures - perhaps bracketing a bit (+1 stop, -1 stop for B&W film) for important shots, but staying with "normal" development.
And just to set the cat among the pigons, I've found the most times after going through the spot metering, previsualizion, and placing zones exercise, I end up with exactly (well +/- 1/2 stop)the same light reading when I use my nikon on matrix metering.
Now I generally just use the Nikons reading, and only play around with the spot metering if I have more time.
I think I'll take your advice. I've been noticing that my exposures have been kinda off since I've been using my camera's metering the last few years. Before that I used to use an incident meter and my exposures were usually right on, plus I'd bracket +/-1 stop. I think the Zone system isn't for my style of shooting, but reading the AA books has helped me previsualize more before shooting. Thanks to everyone for their answers.