I did something similar: made a very small partition on a USB drive and assigned it a drive letter, then tried to install in there. It didn't work because it's the variable that is bigger, not its contents, so whatever value it contains it still overflows the one expected. Short of patching the relevant WINE code (which I don't even know where to start looking for) A XP VM might be the last resort. The software once installed works fine as I experienced by moving to Linux a very old XP install I had on a backup.
