The patch starts to look good, only one tiny thing left: you most likely want to return FALSE from MZ_Exec if CreateProcessA fails.
If you want to read all comments to posts on wine-devel you have to take into account different time zones and different mail reading habits - waiting 24 hours should be enough to get replies from all active readers during weekdays. But, anyway, good to see I didn't scare you by being critical :)