If your rims have braking surfaces, you can add rim brakes front and rear without drilling holes, by taking the arch with bosses off a junk fork and grind/sand/file them to fit your frame, and forks, and then use hose clamps/etc to secure them.
I did this on my CrazyBike2 and SB Cruiser because the fork is alloy, so I couldn't weld them to it. SBC actually has two sets, on in front of the fork and one in back, as it needs a lot of braking power.
viewtopic.php?f=2&t=67833&hilit=brake+a ... 0#p1324787
Ther'es also booster arches you could use, with bolt-on bosses for them. Some info
viewtopic.php?f=2&t=91845&p=1339914&hil ... h#p1339914