No, but when one looks at this logically, one is forced to as WHY?
If you want low powered Windows box, you can certainly buy one cheaper than bastardizing a ReadyNAS. If you are using an old (assuming non-functional) NV+, there isn't an x-86 based MB that I know of that would even come close to fitting. They you are still lacking connectors for a display, and mouse and keyboard. I can buy a cheap new case on line for around $30, add $30 for a PSU and that basically is what you would be avoiding by such a "customization". Looking Newegg, one can put together case, PSU, LGA 1155 MB, Celeron LGA 1155 CPU, 2x1GB memory and DVD burner for less than $200, and you don't have to have pieces outside the case because they won't fit.
I have "customized" regular PC cases in the past, and discovered it is less time intensive and messy to just buy a case that works.
Remember - the NAS is not a backup plan.
Backup = Good, No Backup = Bad