found something that might do the job

http://www.hydrosystemsco.com/brands/hydro/item/hydromaster.html

Anyone any ideas if this would work?

If you are looking to come up with a more dilute delivered solution, make your stock solution more dilute. Any injector is infinitely adjustable via altering the stock solution strength. But then, you may be looking to do something different, what have you got in mind, 1:10, 1:100?

Mazzei makes fertigation injectors that cover a pretty broad range of applications, maybe they have what you need. Their site takes some navigating so, take your time and look through it.

No, I don't have any interest in Mazzei, the company. I am planning to install one of their injectors in my orchard drip system this Spring to see how it works. I've used Dosatron injectors in greenhouses before and like them very much, they are rather expensive though, that's why I've opted for the Mazzei.

Here is a link that might be useful: Mazzei injectors