u can do that by number of steps when you walk pass the subject, or using another person who've walk pass the subject and number of step to reach the point u want to shoot. 1 step is about 1 feet.
Another gauge is when I shoot in a house, each square floor tile is 1 feet.
On the wide angle M lenses, u'll noticed a tab on the focusing ring. when tab is pointing downwards, you're setting distance to 5ft, point to the floor and u'll noticed the distance the floor is somewhat within the treshold (depending on how tall u are).
i've a friend who practised with an RD-1 for a month and he can now shoot w/o looking at the markings, esp for outdoor when you shoot at f4 and smaller.