The thing is if he is asking to nurse when not hungry/thirsty, he must need that connection with you that bfing brings (and you've ruled out boredom too
).
So delaying him or telling him no isn't really going to work any more than telling a child who has fallen and hurt their arm, that you won't give them a cuddle because they had a cuddle earlier in the day, will make them stop crying and learn to self-comfort.
I'm not saying you should martyr yourself to bfing and just let them nurse 24/7 no matter what you are doing/feeling but their needs are important too, and if the child goes through a period of time when they can't (for what ever reason) cope with just nursing twice a day at proscribed times, then perhaps the something that gives is us. We have coping mechanisms that children do not.
Could you try asking your son if he really needs to nurse or if a cuddle or a story snuggled up with you would be ok instead? That way you can give your son another option and he may decide that a story with Mummy would be good or that no bfing is the only thing that will work to help him.
You can also set ground rules like, no nursing if you fiddle, ask nicely (my 2.3y says 'Bah, p'ees Mummy' and has done for a while), no nursing if Mummy is doing X/sitting on X chair (or conversely - if mummy is sitting in the easy chair in the sitting room you can nurse), etc. Being clear and consistent but flexible if the situation demands it helps.
My DDs aren't allowed to bf if I am in the bathroom (after DD1 infamously mugging me when I was sitting on the loo) and I never allow fiddling while nursing but DD3 is allowed to 'honk' while being held as she has done that from tiny and too ill to nurse so I was loathe to stop it
and if they ask it has to be politely (from when they can speak but not before
). They also know if I postpone a feed, I will nurse them when I say I will (e.g. I can't now, I am folding the washing, we will have bah when I have finished and we do). It works well and DD2 is nursing at 4y & DD2 is 2.3y without too many complaints 
I hope you find a way forward that works for all of your family.