If you load a file in Specman via right click on an e file > Run as > Load in Specman, after running the first time, you should find a Run Configuration with the name of the file under the Run > Run Configurations... > Load in Specman group.

You can edit this Run Configuration in order to pass your own Test Commands to Specman. In this specific case, the Test Command field should read:

config gen -default_generator=IntelliGen

You could also use SPECMAN_PRE_COMMANDS system variable (in the console where you run DVT or @user-level):

setenv SPECMAN_PRE_COMMANDS "config gen -default_generator=IntelliGen"

OR

export SPECMAN_PRE_COMMANDS="config gen -default_generator=IntelliGen"