Worthers - as you've realised you need to get hold of the correct attachment. You will not believe how easy and quick an enema is with the correct bit - i.e. long and flexible tube.
I've managed to find one place which sells it seperately (link below). Scroll to the bottom and the last 2 items are both suitable. I have the irrigator tube. Its not all that cheap, but its better than buying a whole new enema kit.