it is possible. some posters have given excellent advice, and i can confirm that 40 miles and additional a little bit cycling to work (which is like easy runs) works fine. i like the furman-first plan, which can be modified easily. 3 days peer week, that is it, but never easy, and some additional cycling for example.
your build up is 6-8 months, that is sufficient if you are used to run. the long run at or close at marathon pace will be a very important part of your weekly schedule. 15 miles at the beginning, but work up to 18 miles and more (and at least five 20 milers). two more purposeful runs (one interval workout and one tempo/threshold run), that is three runs/week. each run is hard and followed by a rest day. after the third run (long run) it is good to have two rest days. if you are getting stronger and you have time for it, try 4-3-4-3 like this for a while:
mo: intervals, tu: rest, we: threshold/tempo, th: rest, fr: tempo, sa: rest, su: long run (4 runs completed), mo: rest, tu: rest (two rest days completed), we: intervals, th: rest, fr: tempo/threshold, sa: rest, su: long run (3 runs completed), 2 consecutive rest days, repeat the whole cycle.
if you are able to pull out intervals like 20x400 or 10-12x3mins and tempo runs of 8-12 miles or 4x15mins at or close to LT pace and long runs like 20 milers at close to marathon pace, you will see that just three quality runs per week like this might be the answer to the question of this thread. it is not the ideal training, but as you have written: some have simply not the time to run every day.