Firstly, it can be done! Secondly, I don't know how...A while ago I had the power lead replaced on my DC04 (by a local vacuum repairer, not a Dyson retailer). He is no longer available and I need to replace it again and have the same problem as you. Brute force doesn't seem to work, just damage the plastic. If I find out I will post the answer; hope you do the same.
William Paul Wride, November 2007