As far as I know, there are no commercial wet mount jigs available for the 4490/v500/v600. This is too bad, considering how many of them are out there (and how badly the engineering of Epson is for this product). I decided to make my own. Here it is......
1 - 1 8x10 clip frame glass ($1-$4 depending where you get it).
2 - Cardboard from a cardboard box of some sort. Thickness to equal .5 to 1 mm, as required.
3 - Cellophane tape.
4 - 1 sheet of acetate (or mylar scanning sheet). Mine cost me $3 at an art store.
5 - Scanning fluid (www.scanscience.com) $25.
6 - 1 microfiber cloth ($1 at a dollar store)
Take the glass out of the clip frame. Cut the cardboard into 1/2 in squares. Tape them onto the 4 corners to form legs. Layer to get optimal height (experiment and adjust). If you use the fluid I suggested, you can use clear acetate, otherwise a sheet of clear mylar will have to be used. Cut a strip big enough to cover a strip of 120, in the usual length. Oversize it enough as it will for a flap covering the film. One edge (length wise) to the sheet glass on the underside (side with the legs) in the center. This has to be just where the stock holders would place the 120 film. You now have a holder.
Flip the acetate back and spray some fluid on the glass. Just enough to have the film stick to the glass. This is not the optical side, so its not that critical. Place the film (emulsion side) onto the glass as square as possible. Spray a healthy amount of fluid onto the film. Experience will dictate how much. Lower the acetate down, going from taped side to end. Take the microfiber cloth and squeeze the air out, going from taped end to the other, while holding the glass from the bottom, just under the film. This gives a gentle pressure from under the glass. You are only concerned with the film itself. You can see some bubbles in the shot above.
To scan, place the holder onto the scanner resting on the cardboard legs. The film never touches the scanner bed. Make sure the holder does not go up to the top edge of the scanner as banding from mis-calibration may result. You will know when you see it. The alignment of the holder is less important and making sure the strip is correctly oriented. It is easier to correct here than in Photoshop.
To remove the film, use a razor knife to pry up the edge of the acetate and then the film. You do not need to re-spay the glass, just the top side of the film as you change strips.
The microfiber cloth is important, because it is soft. The scan surface is the acetate and can be easily scratched. You should expect to replace the acetate from time to time. The glass plate is only required for form and to let the light through. It should be a keeper.
The Lumina fluid is gentle on plastic parts and evaporates off the negs easily. Just expose them to air. The tray, as I have experienced, is not prone to making a mess. I just let it dry on it's own.
Sadly, that's all there is to it. The holder should be generic to any scanner. I can even scan my 110!
Here is an example http://www.flickr.com/photos/peterbcarter/4453982592/ . Choose all sizes to see the full detail.
Well, it's 2015 and I still use the very first one I made. I actually bought a commercial mount but went back to this because it is just easier to use. Sure I moved up to a V700 but it's a generic mount. I figured out that mylar is more expensive than acetate and no more effective. Save your money and just use the acetate. The scanning fluid seems to be the same as odourless clear lamp oil. At $7 a litre, that's what I have been using for the last year.