Ok, overall I think this is a really stupid idea for many reasons, most based on recovery aspects. Bands are no easier to recover from.
First of all, what do you designate as upper back? Traps/rhomboids/rear delts or lats or all of the above? It makes a really big difference in reference to your question. It also depends a lot on your routine. I do two lat movements a week, but through squatting, deadlifting, heavy benching, face pulls, shoulder work, etc. I hit my upper back in some way almost every time I train. There are just too many factors to answer this question without seeing your program/plan.
Now the most I have ever heard of anyone working any bodypart was 4 times a week. I did this with abs, WSB guys have done it with hammies and lats and almost everything, but there is a key to it that most neglect. When you increase frequency you need to pay close attention to your volume, rep schemes, other items in your routine and overall volume. When you move up to high frequency it would be wise to rotate rep ranges and keep the sets low. Most people do 2 sets each day, maybe 3. You have to be careful not to do heavy work before on your upper back before you dead or bench I would argue otherwise if you are sore/stiff you may be unable to stay tight or recruit the proper muscles. Alter the rep ranges. One day do 2 sets of 20 just for a light pump. Another day do 3 sets of 8 with some weight. You get the point. The key in increasing frequency is variation. This is also usually a shorter term thing as well. You wouldn't want to train something 4 times per week with no breaks for 12 weeks or anything. Most of the time when people focus on weakpoint training, they turn down the volume on other things to maintenance levels or just above while the volume is increased for the specific body part and then resume as normal after a micro cycle lasting usually around 3 to 4 weeks. I've seen everyone from Poliquin to WSB do this for weak point training so it is what I followed.
How long you have been training also effects this as well. If you are relatively new, I wouldn't go anywhere near close to that high of frequency on any body part. Hell, most experienced lifters I know will rarely hit something 3 times a week for recovery purposes, even if it is a weakpoint.
Here is what you need to do:
1. Post your current or planned regimen.
2. Clarify what muscle group exactly that you are talking about.
3. State why you want to do this.
If the goal is simply hypertrophy, there are options that I feel would yield better results and have less of a negative impact on a powerlifter or new trainee.