Congratulations on a good career move.
Your boss is not as bad off as you think. I did D1.1 on my CWI exam. It is not so bad. Just have to read it enough times so you know what is where and what isn't there at all. FWIW IMHO the AWS D1.1 seminar is a waste of time and money. The only useful things I got out of it are tabbing your book, and clipping off the metric portions, non-mandatory annexes, and commentary which aren't relevant on the exam. If you subtract the clipped off portions, and the prequalified joints, which you only use a few of, the material you are responsible for is a lot closer between D1.1 and API-1104 than it first seems.
The Welding Inspection Technology part of the seminar should be a breeze. It should just be a review of things you already know. You could probably get by without it.
The Visual Inspection Workshop is great if you have never done visual inspection before. You get to work with tools and plastic imitation weld samples similar to what you will see on the hands on part of the exam. Just be aware that when checking the plastic weld samples for porosity that the porosity on the surface of the samples from the plastic casting process must be ignored. Only the drilled holes, which all happen to be nice multiples of 1/64", count.
Good luck on all three parts. If you don't pass the first time, don't get discouraged. I think most folks probably take it atleast twice before they pass all three parts. I know some that have taken it three times and not passed. Likewise, if you pass, but not high enough to get a CWI, and wind up with a CAWI, don't get discouraged. Keep at it until you get what you are after.