daniel beulshausen from php4win.de told me that there is a sapi independend way to change settings per directory under win32 using the registry:
in "HKEY_LOCAL_MACHINE\SOFTWARE\PHP\Per Directory Values\DRIVE\path\to..."
you can override the ini settings for the specified dir (and all subdirs of course).
the above key doesn't exist, you have to create it. insert only the letter for DRIVE without the ':\'
works fine