Search Google for M5 Well Nuts - very common.
THe Kawasaki Well Nuts look like the left on in this image - it has a ring buldge mid way down and this this is good and bad. Good as it hold the well nut in place and bad as it makes it a lot harder to get one out.
Now here is a good diagram explaiing how they work:
Most of the Well Nuts you will buy do not have the ring/buldge in the middle. They are just straight walled
There are 2 ways to get the the Kawasaki ones out...
1) get a small flat blade screw driver, stick it in the hole. Make sure that the blade is wide enough to push against the brass insert inside - then push the rubber well nut into the hole and then spend 5 minutes finding where it bounced ot if it di actually fall out or get trapped inside somewhere - most of the times they fall out!
2) partially screw in your screw so that it grips the brass thread - and while pullilng on the flange try use the screw to wiggle and with a gentle pull. You cann pull it out just by the screw! Doh! this fattens it up and makes it harder... you have to pull the rubber flange out while using the screw to hold it.
I used method 1) above till I lost one.
After buying 20 well nuts with straight side walls - now you can just easily pull them out.