How do I put current date time (and other non-predefined) variables in info.plist of a Xcode project?

I am trying to put current date & time in the info string of my Xcode project's info.plist. There's no predefined variab开发者_StackOverflow中文版le for this as far as I can see. The best I can think of is to add this to my Run Script:

export MYDATETIME=`date`

And use this as info.plist's Get Info string"

1.0 ${MYDATETIME} Copyright 2011 by Me

That doesn't work since any variables set during Run Script phase don't survive the past the phase. Any way I can make the variable persistent thru the build process?

BTW. The goal is to have the date time stamp as part of the version string.