Hi Pipsmom,
One possibility is to go back to the original and use a different imaging technique. If in the original image there is even the subtlest amout of detail buried in the highlights, then there is hope of extracting it from the image.
Close examination of the compressed JPEG suggest that there is detail yet to be had by better scanning techniques
1) Scan with 16 bit mode and post process in 16 bit mode to see if detail can be brought back out
2) Scan with a scanner/scanner software that allows changing the actual exposure time (length of time exposing the image). This can be used to center the exposure aournd the highlights as a second image and use HDR techniques to combine the two images and restore some details. Some scanning software will do multi-scan HDR for you (or a service provider)
3) Have the image photographed on a copy stand where the exposure is controlled by the lighting and camera
In a worst case if there truly is not detail in the original, there is not that can be done to recover any detail information then you can employ creative alternatives e.g. fill of some sort to make the loss of detail not so noticeable.
Just a suggestion
John Wheeler