All of my affected dogs have let me know if they don't want to be touched in a certain area, you just need to be aware of their body language. Please do not stop showing him affection totally, he will get confused and upset by that. Often they are ok with you touching their chest and rubbing bellies always seems to be popular - quite often rolling over onto the back seems to help anyway [changes in pressure/ flow of the fluid]
IF they do not want to be touched they will very gently turn away, or back away - but it tends to be very slight movements so you need to be aware of it. Don't let other people fuss them roughly either, often "big dog" people tend to be rough with small dogs anyway. Always suggest they put their hand palm up and stroke between the front legs if the dog is happy for them to do that.
My ruby dog, Teddy, who was a real cuddler, couldn't cope with being picked up when he got worse. He [and I] really missed that contact, but he worked out that he could lie across my lap so have that physical contact without it being too painful.
The other thing to remember is that a very light, gentle touch can actually be MORE painful than a firm [but not hard] touch - allodynia - pain that is produced by usually non-painful stimuli.