Hi!
Thanks for posting your solution for that!
I don't think there is another way besides the shutter file to do that, because the type-translation between javascript and the (Java-based) vCenter-Plugin seems to be hardcoded in the vCO-platform (or even in the used Rhino engine). See some other discussions touching that topic here:
http://communities.vmware.com/message/1404592
http://communities.vmware.com/thread/332211
http://communities.vmware.com/message/1810464
However, I don't know any drawbacks when using a shutter-file, besides maybe some decreased security if you open access to too many classes in that file 🙂
Cheers,
Joerg