While surfing on the web, I came across this thread about removing injectors from a 2.2HDi engine. The second post is very interesting:
http://uk.answers.yahoo.com/question/index...226AAIhTy4

Siezed diesel injectors has been a long standing issue on many cars, however there is a company that makes a special injector removing tool, designed for particular engines that attaches to the injector and has a puller fitted and an air powered vibro pack.

Whilst the puller is doing its job an impact hammer is creating a vibration to loosen the corrosion around the injector.

Garages can rent these specialist tools to save making expensive purchases.

http://www.findagarage4u.co.uk/Garage/1475

Don't worry, if you have to take out an injector.
As dCI engines found on Clio/Logan/Duster/etc have injector problems of their own and you'll find quite a lot cars with these engines, then the local garage has for sure an injector removal tool.
I once saw an impact tool similar with a slide hammer.
Something like this:
Only that on our engines that claw piece is not necessary as you can weld on the end of the bar a simple nut that will screw in the injector head where the high pressure line is connected.