I drilled the rubber out, as you start to drill the bit wants to run round the rubber part of the bush, after a few mins and a couple o snapped drills I was through, then cut 2 paralel groves about 10 mm apart right thru the bush outer and chisseled the outer out. about 10 mins each. I used fairy liquid on the polly bushes to help them sit just ticketyboo.
Drew.