Yep - Trimble Grid Factory which we still make available here. There exists a support note from 2009 that I'm trying to source internally as I was able to find it (albeit randomly) on the Internet here. It describes a process for creating a ggf file from data in an Excel sheet.
In addition, I'm poking around internally to see if we have more current utilities that might be able to work with the image format file directly (likely the GeoTIFF). I'll update this thread if I manage to find something.