The answer to the above (I learned this after trying to actually do it) was this: you can not do it.
this is not going to work, not in a decent or acceptable way
There is two type of bolt down post supports like the one I posted in my initial message.
The one that you are looking at in my initial message needs the concrete foot to be around 10" diameter which is huge, it is an overkill.
You can find a smaller one which will almost fit in a 6" diameter concrete foot.
The problem with this last one is that it needs 2 screws on each side (8 for each support) and if you need to align your posts and the post supports everything becomes a nightmare because you have too many things to align for 3 posts in my case
Since my fence segment will attach to the garage at one end and to another post that belongs to the fence that separates us from our neighbor I guess these two ends will add strength to the fence.
These being said I decided to go with this: http://www.rona.ca/en/heavy-duty-spike
We already put these in the ground and installed the posts on top of them and they look solid
The only concern that I have is what will happen when the soil freezes. These posts are three foot long but they are set in a paved area so not much water will get under
The fence was designed to be removable and if these have any problems I will remove them and I will pour concrete footing and I will stick them in concrete :-)
As far as the method to put the bolts into the foot, use this method: cut a thin square piece of plywood, large enough to cover the section of the tube used to form the concrete foot. Put your bolts through it and align their head at the head level. After you pour your concrete, while it is still soft stick the heads of your bolts into it (see the picture above) and rest the plywood on the tube . Make sure everything is aligned as you want. This is how you put multiple bolts into a concrete foot and you maintain everything perfectly aligned. At the end you remove the plywood (cut it, it is not reusable) . Edit: you can make the wholes slightly larger than the bolt and use nuts to adjust the depth of the bolt that will be in concrete. Then you can reuse the plywood. This will introduce some alignment errors. Use a template if you use multiple boards, you will need perfect alginment