Steven, I think you are doing everything you should for Isaac, and Isaac is just being a normal, inquisitve grey - who is just starting to push boundaries! I have suspected for sometime that you love this bird, and heavens, Isaac gets more out of cage time than a lot of birds do. You are dead right though about not just wanting to say "no" to all the forbidden stuff that Isaac has his eye on, but instead, wanting to give him something in it's place. All greys develop differnetly though, and one thing I have observed with Alfie is this. For the last year and a half, Alfie has had no attention span whatsoever, so trying to teach her something to take her mind of whatever she has her eye on at the time has been a non starter - until recently. This might not be the case with Isaac, so instead of giving him a new toy, why not try actually teaching him something, like wave hello or fetch, or whatever. The other thing, Alfie is not into her toys at all. She will play with them when she feels like it, but not very often. She has hundreds of toys that I rotate regularly, but she hardly plays with them, and can go for weeks without playing with any toy at all. She will play with toys that are inside her cage 4 or 5 times more than she will play with them when they are out of it. In light of this, when she is in "one of those" moods when absolutely everything is on her hit list, I put her in her cage and she goes round every single toy in there and knock seven bells out of it!
I have used time outs for Alfie in her travel cage, but that's just for biting. She hasn't bitten in months.
As for keeping Isaac off of stuff that you really don't want him on, like the fridge seal (one of Alfie's favourites too) try hanging something unusual there - like a sock adorning your favourite picture, or a hat on the fridge! Some members have had great success with the old "sock on the door" trick!
I'm not saying any of this stuff will work for Isaac, but it's always something else to try!
Good luck, with this, the next phase in Issacs development. Just enjoy it, for he'll soon move on to the next!!