VMware vCenter Converter Standalone 4.3 can be used to resize powered-on Windows and Linux sources.
Although CentOS is not officially supported as source for Converter 4.3, RHEL 2, 3 , 4 and 5 are so you might work with CentOS as well. No promises though as it has not been tested and officially certified.
See page 52 of the Converter 4.3 Admin Guide at http://www.vmware.com/pdf/convsa_43_guide.pdf for additional information.
