Even if you could fabricate a larger diameter pipe you would still have to find some flexible connectors to suit - which might be the most difficult job, and the reason why Abbott's kit is so pricey. They've probably had to pay for a moulding tool and a small run of mouldings(?)
If you have a 9000 Aero, I wonder if it's really necessary? Dr. Boost and others (myself included) have had pretty good results from just removing the snorkel and drilling a few more holes. There are other areas where the returns are much greater for the dollars/quid spent: exhaust or software to name a few. A 3" downpipe would increase volumetric efficiency and cost much less, for example.
Yeah - £50 for the pipe and £200 for the Abbott sticker! It's tempting to spend the money just because the red sleeve looks so good with the rocker cover. Downpipe is an option but exhaust money is going on a nice oval backbox - standard one is nasty and rusty like every other I have seen!
Anyway, intake pipe is on the back burner until I get rid of the CHECK ENGINE light that has just popped up to say hello.