First of all I want to say thank you for giving a bird in need a second chance and a new home.

Eurycerus wrote:He was with his previous foster dad for six months during which time they clipped him because he was so fearful.
Okay, that's awesome that this man fostered him, and I'm sure he's a great guy, but this is one of the most counter-intuitive things I have ever heard. Could you elaborate on the reasoning behind this decision (if you are able)?
Clipping a fearful bird is only going to make it
more fearful, it's hard for me to understand the rationale here.
Eurycerus wrote:now five days later I thought I'd try to take him out with the pediperch that used to be in his cage ... So after some targeting I brought it out but must have approached too quickly and scared him so much he flapped/fell out of his cage!
Something that the bird is accustomed to can be scary if it's suddenly placed in a different context (the formerly immobile perch from inside the cage is now outside of the cage and is moving).
Obviously you didn't intend to scare him and I'm not admonishing you at all but if you have a fearful bird who is
also clipped you have to avoid causing him to fall at all costs. Every time the bird falls it will greatly reinforce the fearfulness because the bird is confronted with the fact that it is powerless to escape with flight.
Eurycerus wrote:Other than following Michael's guide does anyone have experience with fearful parrots and on methods to gain their trust and work with them? I just want him to be happy.

I don't know how helpful it will be but I will share my experience in case it gives you some ideas. I have a brown-headed parrot who is a rescue. I had never met a more fearful bird. When we went to visit him at the rescue he screamed and fell (he had a bad clip at the time) the moment we entered the room and broke a blood feather.
When we first brought him home he was just terrified of everything. I tried very hard to avoid scaring him but sometimes he would still panic and just fall to the ground like a rock (and usually break a blood feather).
With time he became braver and more confident, noticeably so when his primaries regrew. I have done a lot of positive reinforcement with him using clicker training as well; he seems less fearful now that he knows some tricks. Even though I have had him for 4 1/2 years and he is leaps and bounds ahead of where he was when I first adopted him I still have to walk very slowly when I am carrying him because he startles easily.
Your movements need to be very slow and deliberate when you are around your bird or especially when you approach him. Talk to him constantly in a soft and reassuring voice, tell him what you are going to do
before you do it, and then narrate what you are doing
as you do it. He won't understand what you are saying but I found with my bird this approach made a big difference in the fearfulness.
In the short term while he is still clipped provide him with places he can hide if he gets scared, such as a bird hut or a bird tent even just a hanging cloth or towel. In the long term as you work with him he will hide less and less but for now he should be able to feel like if he's scared he can escape somehow.
I don't know if your bird will tolerate being carried around but if he will give him "tours" of your house. Start small, with just one room. Carry him around and talk to him, walk over to different areas in the room and point to objects and tell him what they are. Give him a treat after the "tour" is finished. Once he is calm taking a tour of one room, take him into another and gradually expand the tour to encompass the whole house. This is another technique I used with my Poi.
You have to walk a fine line with a fearful bird because on one hand you don't want to corner it and force it do things it finds scary (flooding) but on the other hand you have to challenge its threshold somewhat or else it will never get over its fears.