ET45 was just a guess/suggestion, but if that's the case...
You will save money in the long run with narrower tyres. Even going as low as 215 40 won't be any sort of stretch to cause an issue.
And remember, that 40 is a percentage of the width, so 40% of 235mm is marginally increasing the diameter of the tyre as a whole, as well as the extra width, making it all a bit of an ugly fit by the sound of it.
For what it would cost to get your arches rolled properly, you're already talking hundreds. Don't get half a job done on your arches. Plenty of people claim to be able to do it properly, but not many do. Pay cheap and say hello to corrosion in time.
Get a new set of tyres. And seriously consider a set of coilovers if you want to run your tyres close to your arches.