* hold both his hands in mine
Wah! This one I do NOT recommend. Someone thought it would be helpful to stop me picking at my hands by holding them. I knew they meant well but it made me want to smack them. If you're full of nervous energy, someone holding you still is frustrating, annoying, and a bit patronising (it feels like they're being superior over the fact that they have no need to do it and are making a sort of loving protest, like they think they're the Gandhi of skin pickers).
I do stuff like you say your husband does. I don't categorise it as either self-harm or OCD - I've experienced both of those as well, but the kind of things you mention are, to me... well, stress reduction.
Substitutions that help me are to fidget, pick, pull etc at something else instead. Like winding and unwinding a piece of string around my fingers, moulding a piece of blu tack into different shapes, folding and refolding a handkerchief in different ways. I'm not sure what a stress ball is but something they used to sell here was a little stretchy figure that you could pull this way and that and then it would go back into shape - those were good.
I find gnawing and chewing on a liquorice stick better than chewing gum. These are twigs from the liquorice plant, you can get them from some health food shops. It has more of that "worrying at" thing (as in not leaving something alone, but keeping working on it in different ways).
The problem is, though, that your husband needs to want to swap for a different activity. You trying to give him a different activity... I wouldn't do that unless you've previously had a discussion about it and he's agreed to you doing it.
Like I said, I do things like this and I don't think that's self harm. I don't do them to punish myself, to feel pain or to try to shock myself into a different consciousness, which is why I would self harm. These sorts of things are more like extreme fidgeting. In response to extreme stress or distress. They're a form of self-soothing, rather than self-harm.
I personally do want to stop doing them, which is why I try to do other things instead. I wouldn't agree they're a problem to an extent that someone else is justified in intervening. If he doesn't see it as a problem, why do you want to change it? If you don't like watching it, don't look.