[PoP]

Cleaned up a bit. Added a third style with rounded corners. Passes through all other fbink parameters. {but still inefficient}

Spoiler:

cd /mnt/us
#expects PATH=$PATH:.
S=1
box -x 0 -y 0 -S $S -T " AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789!\"#$%&'()*+,-./:;<=>?@[\\]^_\`{|}~" -c 
screenshot

box -x 0 -y 0 -S $S  -T " AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789!\"#$%&'()*+,-./:;<=>?@[\\]^_\`{|}~" -c -Fk 0
screenshot

box -x 0 -y 0 -S $S  -T " AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789!\"#$%&'()*+,-./:;<=>?@[\\]^_\`{|}~" -c -Fd 1
screenshot

box -x 0 -y 0 -S $S  -T " AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789!\"#$%&'()*+,-./:;<=>?@[\\]^_\`{|}~" -c -Fd 1 -Fk 0
screenshot

box -x 0 -y 0 -S $S  -T " AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789!\"#$%&'()*+,-./:;<=>?@[\\]^_\`{|}~" -c -Fd 3
screenshot

box -x 0 -y 0 -S $S  -T " AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789!\"#$%&'()*+,-./:;<=>?@[\\]^_\`{|}~" -c -Fd 3 -Fk 0
screenshot

[EDIT 2018-09-28] Further cleanup, Quoted blank expansions, Silenced fbink.