got these working. The keys were not having anything other than the freeze.bat script in the backupscripts.d folder. Then - while I'm not sure of the effect, command order in the script seemed to matter so that my script was only partially executing when called during backup.
Here's the reference KB: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006671
Here's a good blog on the technique: http://www.bluemunkey.com/?p=338
Here are working scripts using diskshadow - which is already installed, modifying the blog approach slightly:
##freeze.bat##
del c:\windows\metadata\backup.cab
C:\Windows\System32\diskshadow -s c:\windows\shadowScript.txt
date /t >> c:\windows\metadata\callme.txt
time /t >> c:\windows\metadata\callme.txt
##shadowScript.txt##
delete shadows all
reset
set context persistent
add volume c: alias new1
add volume g: alias new2
set metadata c:\windows\metadata\backup.cab
create