Greetings Skikick,
I took a look at what Sheldon said. Yes I have done that. To avoid re-dishing the rim, I added washers and both sides of the hub or if you have access to hub locking nuts, I often just use wider locking nuts on both sides of the hub. This also basically makes the whole assembly wider, so what people often do is just jam the wheel in the frame. This adds extra stress on the frame when riding, which could cause frame failure. So it is recommended that you spread the frame so the wheel fits properly. This can be difficult to do properly.
The other option is to re-space the hub and re-dish the wheel to work with 7 speed free wheels or cassettes and fit the wheel in the frame as it is. I have done this as well.