[NTG-context] redirecting temp files (MkII)

Hi all, I use the XeTeX/ConTeXt MkII combi as part of another application. This (Windows) application is installed in the C:\Program Files tree which apparently is marked 'read only' in Vista/Windows 7. Would it be possible to redirect the temp files (*.top, *tui, *.log, *.mp) to a different folder outside C:\Program Files\ ? Texexec.rb comes with an option --tempdir= but that doesn't work. Thanks, Jelle