A few years ago I has the same problem and got my local garage, who I've used for years, to do a proper 4 wheel alignment. The mechanic told me that he'd gone for 0 degrees on the front wheels and also made sure that the front and back wheels were parallel as he reckons that this is generally best for cars (he's been in the business 30 plus years).
Since then I've never had a set of tyres noticeably wearing unevenly, even after having the front and rear shocks and springs done last year.
I'd recommend spending the little bit extra having proper 4 wheel alignment done and get the front wheels set at 0 degrees, cheaper than replacing tyres halfway through their life!