Then no, there is no alternative to a catheter. But they will put it in while he is unconscious so he won't be aware of it being done.
Basically, they cut the urethra during the op, remove the prostate with some urethra running through the middle of it and then join the 2 cut ends of urethra back together. That join must be protected for a week or two until it heals, so the catheter stops urine leaking into his body through the stitched join. It might be that whoever did his catheter last time used a big one - the surgeons are very experienced in this stuff and would not give him something too large for his body. It can be a bit uncomfortable at the end of the penis - it gets a bit red and sore - but your uncle can ask the hospital for some local anaesthetic gel to avoid this. It would also help if he asks the nurse to show him how to strap the catheter during the day and at night - the two are different.