Cant be done from the Adminstrator Console, but it can be done from SQL console...I got this information from Symantec installation engineer during our implementation engagement.
Create a text list of all the computers you want to search, one per line (i.e. export list of computers from AD Organization Unit)
Then take that list and create an SQL query file with the following commands:
declare @@computername as varchar(100)
declare @@computername1 as varchar(100)
declare @@computername2 as varchar(100)
... (for as many computers as you have)
set @@computername='comp'
set @@computername1='anothercomp'
set @@computername2='yetanothercomp'
... (for as many computers as you have, each machine name listed in single quotes, one per line)
declare @@searchable as varchar(100)
set @@searchable = '1'
USE EnterpriseVaultDirectory
Update PSTComputer Set SearchThisComputer=@@searchable Where Computername=@@computername
Update PSTComputer Set SearchThisComputer=@@searchable Where Computername=@@computername1
Update PSTComputer Set SearchThisComputer=@@searchable Where Computername=@@computername2
... (for as many computers as you have)
Run this from SQL Query Analyzer.