Could you not get the Éclat alloys re-drilled 4x100 (45 degrees to the existing PCD)? Then you can obviously loose the spacers. Although the rims I had on my Aerodeck were 7J et25 and they were perfect in my opinion.
Without adjustable rear arms...

With adjustable rear arms...

I looked into arch extensions as well. I think I worked out that Celica Supra arches were going to be too big. I thought Peugeot 309 Gti Ecosse Milano arches were a possibility... They even look to be the correct shape...
http://www.ecosse-peugeot.co.uk/show_pr ... 62&appid=7
Struggling to find a proper picture, but this guy modified a set to fit his 4 door...

There was a fibre glass company making cheaper replicas on ebay once, but they seemed to stop advertising them and their communication was rubbish sadly.