Another poop dilemma

My 3.5 year old toddler is very happy to do his wees in the loo, but not the no.2's.  He is not afraid of sitting on the loo as when I think something is coming I sit him there but he won't let it out or has pulled back so hard that it won't come out.  Then after about 20 minutes of this I let him off and later he does it - just not on the loo!  It is a great ploy from his side to get one2one attention of which I am aware, though he gets plenty attention anyway so he shouldn't have to.  The worst of all though is that it is an unnecessary issue in his mind.   I hope somebody out there has a novel idea I might try!

Toilet training is a traumatic time for some toddlers! Fortunately my girl sort of did it all herself- though to be honest some of it was attention seeking as there was a brand new baby in the house- but I didn't mind! LOL! Anyway, my friends little boy was like that (maybe its a boy thing?) and her Health Visitor told her that a lot of children are terrified by the sensation of doing a poo, they think their insides are falling out- which you could see might be terrifying! She advised to get him to do his poo on a potty, then show him it and carry it to the loo and show him that thats where its supposed to go, then let him flush the loo to get rid of the 'stinky'? This worked for her in a few days! If it didn't, try a reward chart- he gets a star for every poo he does on the toilet, and for every 5 or so he gets a treat? Good luck!