From our good friends at e-on, this is how you do it:

To recover .tmp tile files, please run Vue with the following command line option:

Vue 6 Infinite.exe -t"[PATH TO YOUR DIRECTORY HOLDING TMP FILES]"

for example, if your tmp files are in "c:/TmpFilesDir", you have to launch Vue with:

Vue 6 Infinite.exe -t"c:/TmpFilesDir/"

Make sure you have a trailing slash on the directory name or it will not work! It took me about five times to get it right.