Hmmm... All you have to do is convert to the velvia profile. Scanner and Camera profiles from Gretag, which are essentially the same, are one way profiles. You can only convert from them, not to them. Have you actually done this or is just theory because I can only assign camera or scanner profiles to an existing image.
Eye-One camera camera profiles are basically a color transform from film color to calibrated accurate color, using the scanner's output space as a baseline. If your scanner outputs ProPhoto and you used a Velvia scan to build the profile, when you assign the Velvia profile to a Velvia scan and then convert to ProPhoto, you have converted Velvia's color palette to calibrated, accurate color. This is of course the opposite of what the OP wants.
Scanner and Camera profiles from Gretag, which are essentially the same, are one way profiles. You can only convert from them, not to them.
False. Just because that's the standard, "intended" use for such a profile doesn't mean it's the only
way to use it. If you take a calibrated-color ProPhoto image, convert it to the Velvia profile, and then assign ProPhoto to the image (instead of assign, then convert), you have reversed the effect of the profile so that calibrated, accurate colors are converted to Velvia's color palette and tone curve, instead of the other way around.
You can expand this technique to give a shot made with one film the look of a different film (except for the grain pattern, of course). Let's say you have made profiles for your scanner and Reala and Velvia films, using ProPhoto as your scanner output space. You have an Reala shot but you wished you had used Velvia instead. Here's how you convert to the color look of the other film:
1: Assign the Reala profile to the Reala shot, which should be tagged with ProPhoto. Without changing the RGB values, this step redefines the meaning of the RGB color values so that they display as accurate, calibrated color.
2: Convert the image to the Velvia profile. This will alter the RGB values so that the color channel values are exaggerated, but simultaneously redefine the meanings of those RGB values so that accurate colors are still displayed.
3: Assign ProPhoto to the image. It will now have Velvia's color palette and contrast curve.