Yes!
Arm day:
1)Do 21's last as a finishing exercise
2)Do one triceps exercise followed by a bicep exercise
Example:
Biceps: Preacher Curl, 21's
Triceps: Close Grip Bench Press, Skull Crushers
CGBP - Preacher Curl - Skull Crusher - 21's - CGBP - Preacher Curl - Skull Crusher - 21's - CGBP - ...
Like illustrated in this video
Just scaled down so to say, as you can't do a killer workout every week (;
So instead of the hour long workout or so
=>Rest 45-90 seconds between sets depending on rep range (more reps = less rest)
=>Do 3-5 sets in total for every exercise