I believe I have heard of it being done. 225's in Kumho's are skinnier than 225 Hoosiers and I have heard (HEARD mind you) that if you flare the fender wells a bit and accept that you can not turn near wheel lock you can get 225 R15 Hoosiers on. A 205 Hoosier is about the width of a 225 Kumho. Same goes for the Hankook Z214's at 225 compared to a Hoosier 205.

There might be some rub though on the rear trailing arms which is why I have also heard in order to be able to run 225 R15's you need a large spring rate in the rear (heard 1000#'s). This is to prevent the car from leaning over the tire and instead lean the tire over with the lean of the car. It is also nick-named knife edge driving at that spring rate because the car will tend to hook around corners but if you get it wrong you end up pointed the wrong way.