Wow, thanks for all the answers! Sorry I could not come back sooner; I was away at a workshop with very very little internet acces (I really cannot do much with an iPod when the only connexion available is through an Ethernet cable...!)

I know the simplest answer is to do it with a camera, and even if I do have access to an 8x10 though a local shop, the rental cost would be too much. It would be either the camera OR the negatives

What I do have is an enlager & IC timer; and I must have an 80a or b lying around somewhere. It seemed rather straight forward in theory, but [COLOR=#444444]grahamp seem to suggest that it would not be such a good way to go, especially with the regular, non-shutter obturator. Has any other person ever tried it? Doremus? I am wondering why it'd work nicely with paper and not film... Is it the the iso difference that makes it more harder to find the right exposure? If it would, then the 80a/b would cut around 2 stops, making my portra 160 feel like an iso 40. I could further cut the light with a light ND filter...
The other solution that could make sense for me would be to build an 8x10 pinhole camera, as suggested. I have never done it, but there are more than plenty DIY for it on the net, and a flash on a white wall is quite easy to provide.

Thanks ic-racer; I did not know about it. From what I understood, though, for this application it would be too bright. I'd need lots of neutral density to filter it! But it's good to know they exist and are so inexpensive

Thanks again for your help!