You'd need a fairly long hood to reduce the reflections on the glass.
You might want to look into an iMac Matte film for the screen, not too sure how effective they are as you have 2 reflective surfaces. Other less practical option seems to be repositioning the iMac.
After that your limited to a Mac Pro or Mac Mini (or Macbook and a decent Matte monitor)
let me tell you first that you are in my shortlist, way up, for best nick in the fora!
I have a mac mini brother, which I bought to avoid the horrible glare of the imac, but I am considering exchanging it for an imac if a hood does the job (since I 've not been satisfied with the available coating screen tec), but as you pointed out (good point btw) you have two reflective surfaces to begin
with so I dunno if they 'd be of much help.
For anyone such as myself with glare issues and eye problems font size and clarity is a must, sadly the screen tech is still lagging for an ideal solution.
It might be of interest to a lot here this article which I found extremely helpful to go over what options there are for sensitive people.
http://www.pcmonitors.org/articles/matte-vs-glossy-monitors#!prettyPhoto[gallery-BenQ low-haze (PC on)]/0/
Sadly apple's enormous amount of cash in the bank isn't apparently going into some decent funding of research and the prefer to just stick a glass on top of the imacs that makes things even worse. I am getting very pissed off with them recently what with lion sucking so badly and not bringing resolution independence for some clear bigger fonts for those who need it and claiming they will have an hdpi support when the screens, whenever... Heck, they didn't even bother raising the default font max size from 16 on the desktop on lion despite the dire need after the very high dpi of 27" imacs, and lappies...
In the meantime until they sort the glass issues and until they have hdpi screens we get glassy glares and fonts like ants on the 27" imac and transposing the problem to screen manufacturers with the mini and pro... and bs cut and paste ergonomic how to's (
http://www.apple.com/about/ergonomics/vision.html ) with images of users seating in front of crt screens like every other dime a dozen ergonomics vendor has...
Anyway, if anyone is using a hood on an imac with some success I d love to hear first hand experiences.