Overlapping Insurance

I was insured on my SR for a year beginning December 2008
In September 2009 I passed my test, broke the SR, bought the CB.

Ebike, with whom I was insured on the SR, wanted an extortionate amount to insure the CB, so I took out a new policy with Adrian Flux for it.
For the three months Sept-December I was therefore insured on both bikes.

I’m presuming that the years for a no claims bonus don’t count if they overlap, but I’m also aware that short-term insurance is generally extortionate. Is there a way of proceeding that’s likely to end up with me saving money, or should I just keep renewing in September?

My first thought is to ask AF if they’ll ‘extend’ the policy by three months now and let me renew in December, but if the main aim is to make next year cheaper, I would expect refusal. Are there any other companies likely to do that? AF’s renewal for next year is ~10% cheaper than any quotes I can get from anywhere else from a quick comparison site excercise.