well this is sort of what you want, and it may help.
Have a look at Example PstLocatorTask.exe.config - its in the Enterprise Vault install directory.
There is a specific section called "sharestoavoid"
If it's suitable for what you want - save the file as PstLocatorTask.exe.config - and restart the PST Locator task.
Apart from that - there is no other way to do it.