On Monday, March 2, 2015 at 4:24:08 PM UTC, Robin wrote:
sm_jamieson wrote:
The *best* solution may be to purchase something specific. However I
usually end up tweaking something genetic that I have. So, normal
rawlplugs, just cut off the rim. If you want a "sheath" all the way
up, a cheap frame fixing (e.g. from toolstation), trimmed to suit.
Simon.

Thanks. I see the merits of that if it's just the odd job - though I'm
put off by my incompetence which means I've all too often nicked a
finger doing it with whatever wrong tool was at hand
--

Yes, maybe you can get a special tool to do it ;-)
I find electrical side cutters do the job. And the trick with a stanley knife is to "wobble" the blade through the plastic rather than trying to "slice" it and risk the knife slicing you too. Or, hold the knife steady and pull the item past it.
Simon.