With a fix.dat : Load the fix.dat, it is more or less the same as a normal dat only with the set/roms that are missing. Create a folder on your PC and set the rom-path to thjis folder. Now you can use the "rebuilder" and choose the rom-folder you want to search for your missing and check that the destination-folder is the new created folder. There it will store the file that it has found in the rom-folder ......please be sure that you have unticked "removed matched sourcefile" (it should be greyed out with a fix.dat). Otherwise it would remove found files in the source-folder .....
All missing sets/roms that have beend found are now in The new created folder .....repeat the steps again if you have still missing or want to scan another source folder ....
this new folder can be used for your friend to rebuild his folder. (source: new folder, desitination:Friends rom folder). Be sure that you enable "backup" in the scan-option before removing old files ...
that was a quick answer, it is early in the morning -> you can also check my guide at mameguide.info. There is also a section for CLRMAMEPro.