ET35. I personally haven't seen a set about in the U.K yet so I'm determined to get them to fit so that I'll not have a set that a million other people have. So if it comes to it they'll be welded and re-drilled
Welded and redrilled is your best bet then I would imagine.
Adaptor spacers are likely to be around 20mm wide and in the case of a 9" wide rim in the first place its already going to be sat quite far out, so thats likely to be too much.
you could also consider redrilling the disks and hubs instead of the wheels, so that you basically make your car multifit in the first place.
Im always messing around with different rims on our cars as like you my mrs just likes having stuff thats not the same as everyone elses, this is my mrs old mk1 on vauxhall cesaro wheels, and this is some scooby wheels I am using at the moment for mocking up some adaptors as she has seen some scooby rims she likes the look of (not actually these ones, but I had these handy to use for the templates)
What center bore are your rims?
On the cesaros even though they are 4*100 I had to make adaptors due to the spigot size being smaller than the renault and as we have several sets (wets dries etc) I didnt want to bore the wheel itself, plus I was correcting the offset too.