Unfortunately, there is no feature to change the minimum number of characters for helpdesk recovery at this time.
There are a couple of feature requests out there that are similar to what you are asking for. One of the requests is to redue the minimum number of characters for the recovery questions. However, if that feature were to be implemented, I would assume they would put in some sort of selection process rather than just reducing the minimum requirements.
I recommend subscribing (subscribe via e-mail link on top right) to the feature requests that way you can receive an e-mail update of either of them are implemented.
FEATURE REQUEST: Allow Symantec Encryption Management Server Admins control over Security Questions for Key Reconstruction - http://www.symantec.com/docs/TECH215165
FEATURE REQUEST: Reduce the required number of characters required for Key Reconstruction from 6 to 4 - http://www.symantec.com/docs/TECH215164