The script would take many of the steps into consideration like checking out the code and setting up cygwin. More importantly it should prompt the user for environment variable values that the Windows build needs. In particular, WEBKIT_OUTPUTDIR, WEBKIT_LIBRARIES, WEBKIT_TESTFONTS, and WEBKIT_SOURCE. I think this would be a useful endeavor after finishing the VS2010 setup as I'm changing some of the environment variable names and adding an extra one. VS2010 setup also needs some values to be added environment Path variable.
<rdar://problem/13026334>
Note that WebKitDirs.pm currently performs this function. I think you should extend it to cover the new values you mention in the bug description, but it might be helpful to create a simple Perl script that calls WebKitDirs.pm functions to perform the steps outside of the update-webkit world.