A simple martial arts belt or rope has a bit of give in them and a towel can work or a pool noodle.
The inlocate is sort of necessary for front giant, or swinging in eagle grip. Yes, gymnastics asks for more flexibility than is necessary when it comes to shoulders, especially on rings or HB. Either do it or don't really.
I think with the very inflexible, we simply have to grind those tight muscles out. One of my boy's is very inflexible in his shoulders and it depreciates his tumbling potential. His basics suck and while this poor flexibility doesn't hamper him on rings, it does on High Bar and for back and front tumbling. Were going through a lot of shoulder mobility but he may also be further helped by going to an ART practitioner. He's not 10 yet, so he still has a good chance of developing flexibility but it's gonna be slow. As well he has poor flexibility in his legs as well. At least he is beastly strong for a lil guy ( 52 pounds ).
Otoh, I have another boy who can do dislocates at shoulder width. He can hang on rings and inlocate in or dislocate out from the bottom of a skin the cat with no pain. In his case, especially when training the ring inlocate he will need to do band dislocates. As well he never feels anything in the shoulder mobility we do compared to the other guy who is nearly in tears ( like me! ). It's almost pointless but as he is getting stronger we will need to keep that flexibility since it is what his potential for many skills quite awesome ( as weak as he is, presses are not a problem though he is barely strong enough to hold a straddle L ).