Hi Jaffa,
Seeing your paediatrician (and being totally honest ) sounds like a good first step, and get treatment for any skin irritation. Naturally there are a lot of sensory issues involved with this. Does your son have any other learning or cognitive difficulties? it's going to be hard to find a replacement for this convenient, and pleasurable, activity as your son gets older so it's good to address it now. Has he seen an OT - do you have a sensory diet? Other sensory input may help to reduce the need to 'play' - fidget toys and other distractions that keep hands busy are a good strategy. He may also benefit from daily sensory input activities like heavy work, linear movement (bouncing, swinging, trampoline), deep pressure, weighted therapy, you should be guided by your OT. Remember a sensory diet is like a food diet, it won't work if you just stick it on the fridge door, you have to follow it every day.
Also make sure you include specific teaching, about private and public, esp. if there is a learning disability. If this doesn't work you may need to try to get a behavioural psychologist involved.

Bernadette.